Table of Contents
The MySQL Performance Schema is a feature for monitoring MySQL Server execution at a low level. The Performance Schema has these characteristics:
The Performance Schema provides a way to inspect internal
execution of the server at runtime. It is implemented using the
PERFORMANCE_SCHEMA storage engine
and the performance_schema database. The
Performance Schema focuses primarily on performance data. This
differs from INFORMATION_SCHEMA, which serves
for inspection of metadata.
The Performance Schema monitors server events. An “event” is anything the server does that takes time and has been instrumented so that timing information can be collected. In general, an event could be a function call, a wait for the operating system, a stage of an SQL statement execution such as parsing or sorting, or an entire statement or group of statements. Event collection provides access to information about synchronization calls (such as for mutexes) file and table I/O, table locks, and so forth for the server and for several storage engines.
Performance Schema events are distinct from events written to the server's binary log (which describe data modifications) and Event Scheduler events (which are a type of stored program).
Performance Schema events are specific to a given instance of the MySQL Server. Performance Schema tables are considered local to the server, and changes to them are not replicated or written to the binary log.
Current events are available, as well as event histories and summaries. This enables you to determine how many times instrumented activities were performed and how much time they took. Event information is available to show the activities of specific threads, or activity associated with particular objects such as a mutex or file.
The PERFORMANCE_SCHEMA storage
engine collects event data using “instrumentation
points” in server source code.
Collected events are stored in tables in the
performance_schema database. These tables can
be queried using SELECT
statements like other tables.
Performance Schema configuration can be modified dynamically by
updating tables in the performance_schema
database through SQL statements. Configuration changes affect
data collection immediately.
Tables in the Performance Schema are in-memory tables that use no persistent on-disk storage. The contents are repopulated beginning at server startup and discarded at server shutdown.
Monitoring is available on all platforms supported by MySQL.
Some limitations might apply: The types of timers might vary per platform. Instruments that apply to storage engines might not be implemented for all storage engines. Instrumentation of each third-party engine is the responsibility of the engine maintainer. See also Section 22.19, “Restrictions on Performance Schema”.
Data collection is implemented by modifying the server source code to add instrumentation. There are no separate threads associated with the Performance Schema, unlike other features such as replication or the Event Scheduler.
The Performance Schema is intended to provide access to useful information about server execution while having minimal impact on server performance. The implementation follows these design goals:
Activating the Performance Schema causes no changes in server
behavior. For example, it does not cause thread scheduling to
change, and it does not cause query execution plans (as shown by
EXPLAIN) to change.
No memory allocation is done beyond that which occurs during server startup. By using early allocation of structures with a fixed size, it is never necessary to resize or reallocate them, which is critical for achieving good runtime performance.
Server monitoring occurs continuously and unobtrusively with very little overhead. Activating the Performance Schema does not make the server unusable.
The parser is unchanged. There are no new keywords or statements.
Execution of server code proceeds normally even if the Performance Schema fails internally.
When there is a choice between performing processing during event collection initially or during event retrieval later, priority is given to making collection faster. This is because collection is ongoing whereas retrieval is on demand and might never happen at all.
It is easy to add new instrumentation points.
Instrumentation is versioned. If the instrumentation implementation changes, previously instrumented code will continue to work. This benefits developers of third-party plugins because it is not necessary to upgrade each plugin to stay synchronized with the latest Performance Schema changes.
The MySQL sys schema is a set of objects that
provides convenient access to data collected by the Performance
Schema. In MySQL 5.7, the sys schema is
installed by default. For MySQL 5.6, you can obtain it from the
schema development website at
https://github.com/mysql/mysql-sys. For usage
instructions, see MySQL sys Schema.
This section briefly introduces the Performance Schema with examples that show how to use it. For additional examples, see Section 22.18, “Using the Performance Schema to Diagnose Problems”.
For the Performance Schema to be available, support for it must
have been configured when MySQL was built. You can verify whether
this is the case by checking the server's help output. If the
Performance Schema is available, the output will mention several
variables with names that begin with
performance_schema:
shell> mysqld --verbose --help
...
--performance_schema
Enable the performance schema.
--performance_schema_events_waits_history_long_size=#
Number of rows in events_waits_history_long.
...
If such variables do not appear in the output, your server has not been built to support the Performance Schema. In this case, see Section 22.2, “Performance Schema Build Configuration”.
Assuming that the Performance Schema is available, it is enabled
by default. To enable or disable it explicitly, start the server
with the performance_schema
variable set to an appropriate value. For example, use these lines
in your my.cnf file:
[mysqld] performance_schema=ON
When the server starts, it sees
performance_schema and attempts
to initialize the Performance Schema. To verify successful
initialization, use this statement:
mysql> SHOW VARIABLES LIKE 'performance_schema';
+--------------------+-------+
| Variable_name | Value |
+--------------------+-------+
| performance_schema | ON |
+--------------------+-------+
A value of ON means that the Performance Schema
initialized successfully and is ready for use. A value of
OFF means that some error occurred. Check the
server error log for information about what went wrong.
The Performance Schema is implemented as a storage engine. If this
engine is available (which you should already have checked
earlier), you should see it listed with a
SUPPORT value of YES in the
output from the
INFORMATION_SCHEMA.ENGINES table or
the SHOW ENGINES statement:
mysql>SELECT * FROM INFORMATION_SCHEMA.ENGINESWHERE ENGINE='PERFORMANCE_SCHEMA'\G*************************** 1. row *************************** ENGINE: PERFORMANCE_SCHEMA SUPPORT: YES COMMENT: Performance Schema TRANSACTIONS: NO XA: NO SAVEPOINTS: NO mysql>SHOW ENGINES\G... Engine: PERFORMANCE_SCHEMA Support: YES Comment: Performance Schema Transactions: NO XA: NO Savepoints: NO ...
The PERFORMANCE_SCHEMA storage engine
operates on tables in the performance_schema
database. You can make performance_schema the
default database so that references to its tables need not be
qualified with the database name:
mysql> USE performance_schema;
Performance Schema tables are stored in the
performance_schema database. Information about
the structure of this database and its tables can be obtained, as
for any other database, by selecting from the
INFORMATION_SCHEMA database or by using
SHOW statements. For example, use
either of these statements to see what Performance Schema tables
exist:
mysql>SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLESWHERE TABLE_SCHEMA = 'performance_schema';+----------------------------------------------------+ | TABLE_NAME | +----------------------------------------------------+ | accounts | | cond_instances | | events_stages_current | | events_stages_history | | events_stages_history_long | | events_stages_summary_by_account_by_event_name | | events_stages_summary_by_host_by_event_name | | events_stages_summary_by_thread_by_event_name | | events_stages_summary_by_user_by_event_name | | events_stages_summary_global_by_event_name | | events_statements_current | | events_statements_history | | events_statements_history_long | ... | file_instances | | file_summary_by_event_name | | file_summary_by_instance | | host_cache | | hosts | | mutex_instances | | objects_summary_global_by_type | | performance_timers | | rwlock_instances | | session_account_connect_attrs | | session_connect_attrs | | setup_actors | | setup_consumers | | setup_instruments | | setup_objects | | setup_timers | | socket_instances | | socket_summary_by_event_name | | socket_summary_by_instance | | table_io_waits_summary_by_index_usage | | table_io_waits_summary_by_table | | table_lock_waits_summary_by_table | | threads | | users | +----------------------------------------------------+ mysql>SHOW TABLES FROM performance_schema;+----------------------------------------------------+ | Tables_in_performance_schema | +----------------------------------------------------+ | accounts | | cond_instances | | events_stages_current | | events_stages_history | | events_stages_history_long | ...
The number of Performance Schema tables increases over time as implementation of additional instrumentation proceeds.
The name of the performance_schema database is
lowercase, as are the names of tables within it. Queries should
specify the names in lowercase.
To see the structure of individual tables, use
SHOW CREATE TABLE:
mysql> SHOW CREATE TABLE performance_schema.setup_consumers\G
*************************** 1. row ***************************
Table: setup_consumers
Create Table: CREATE TABLE `setup_consumers` (
`NAME` varchar(64) NOT NULL,
`ENABLED` enum('YES','NO') NOT NULL
) ENGINE=PERFORMANCE_SCHEMA DEFAULT CHARSET=utf8
Table structure is also available by selecting from tables such as
INFORMATION_SCHEMA.COLUMNS or by
using statements such as SHOW
COLUMNS.
Tables in the performance_schema database can
be grouped according to the type of information in them: Current
events, event histories and summaries, object instances, and setup
(configuration) information. The following examples illustrate a
few uses for these tables. For detailed information about the
tables in each group, see
Section 22.12, “Performance Schema Table Descriptions”.
Initially, not all instruments and consumers are enabled, so the performance schema does not collect all events. To turn all of these on and enable event timing, execute two statements (the row counts may differ depending on MySQL version):
mysql>UPDATE performance_schema.setup_instrumentsSET ENABLED = 'YES', TIMED = 'YES';Query OK, 338 rows affected (0.12 sec) mysql>UPDATE performance_schema.setup_consumersSET ENABLED = 'YES';Query OK, 8 rows affected (0.00 sec)
To see what the server is doing at the moment, examine the
events_waits_current table. It
contains one row per thread showing each thread's most recent
monitored event:
mysql>SELECT *FROM performance_schema.events_waits_current\G*************************** 1. row *************************** THREAD_ID: 0 EVENT_ID: 5523 END_EVENT_ID: 5523 EVENT_NAME: wait/synch/mutex/mysys/THR_LOCK::mutex SOURCE: thr_lock.c:525 TIMER_START: 201660494489586 TIMER_END: 201660494576112 TIMER_WAIT: 86526 SPINS: NULL OBJECT_SCHEMA: NULL OBJECT_NAME: NULL INDEX_NAME: NULL OBJECT_TYPE: NULL OBJECT_INSTANCE_BEGIN: 142270668 NESTING_EVENT_ID: NULL NESTING_EVENT_TYPE: NULL OPERATION: lock NUMBER_OF_BYTES: NULL FLAGS: 0 ...
This event indicates that thread 0 was waiting for 86,526
picoseconds to acquire a lock on
THR_LOCK::mutex, a mutex in the
mysys subsystem. The first few columns provide
the following information:
The ID columns indicate which thread the event comes from and the event number.
EVENT_NAME indicates what was instrumented
and SOURCE indicates which source file
contains the instrumented code.
The timer columns show when the event started and stopped and
how long it took. If an event is still in progress, the
TIMER_END and TIMER_WAIT
values are NULL. Timer values are
approximate and expressed in picoseconds. For information
about timers and event time collection, see
Section 22.4.1, “Performance Schema Event Timing”.
The history tables contain the same kind of rows as the
current-events table but have more rows and show what the server
has been doing “recently” rather than
“currently.” The
events_waits_history and
events_waits_history_long tables
contain the most recent 10 events per thread and most recent
10,000 events, respectively. For example, to see information for
recent events produced by thread 13, do this:
mysql>SELECT EVENT_ID, EVENT_NAME, TIMER_WAITFROM performance_schema.events_waits_historyWHERE THREAD_ID = 13ORDER BY EVENT_ID;+----------+-----------------------------------------+------------+ | EVENT_ID | EVENT_NAME | TIMER_WAIT | +----------+-----------------------------------------+------------+ | 86 | wait/synch/mutex/mysys/THR_LOCK::mutex | 686322 | | 87 | wait/synch/mutex/mysys/THR_LOCK_malloc | 320535 | | 88 | wait/synch/mutex/mysys/THR_LOCK_malloc | 339390 | | 89 | wait/synch/mutex/mysys/THR_LOCK_malloc | 377100 | | 90 | wait/synch/mutex/sql/LOCK_plugin | 614673 | | 91 | wait/synch/mutex/sql/LOCK_open | 659925 | | 92 | wait/synch/mutex/sql/THD::LOCK_thd_data | 494001 | | 93 | wait/synch/mutex/mysys/THR_LOCK_malloc | 222489 | | 94 | wait/synch/mutex/mysys/THR_LOCK_malloc | 214947 | | 95 | wait/synch/mutex/mysys/LOCK_alarm | 312993 | +----------+-----------------------------------------+------------+
As new events are added to a history table, older events are discarded if the table is full.
Summary tables provide aggregated information for all events over
time. The tables in this group summarize event data in different
ways. To see which instruments have been executed the most times
or have taken the most wait time, sort the
events_waits_summary_global_by_event_name
table on the COUNT_STAR or
SUM_TIMER_WAIT column, which correspond to a
COUNT(*) or SUM(TIMER_WAIT)
value, respectively, calculated over all events:
mysql>SELECT EVENT_NAME, COUNT_STARFROM performance_schema.events_waits_summary_global_by_event_nameORDER BY COUNT_STAR DESC LIMIT 10;+---------------------------------------------------+------------+ | EVENT_NAME | COUNT_STAR | +---------------------------------------------------+------------+ | wait/synch/mutex/mysys/THR_LOCK_malloc | 6419 | | wait/io/file/sql/FRM | 452 | | wait/synch/mutex/sql/LOCK_plugin | 337 | | wait/synch/mutex/mysys/THR_LOCK_open | 187 | | wait/synch/mutex/mysys/LOCK_alarm | 147 | | wait/synch/mutex/sql/THD::LOCK_thd_data | 115 | | wait/io/file/myisam/kfile | 102 | | wait/synch/mutex/sql/LOCK_global_system_variables | 89 | | wait/synch/mutex/mysys/THR_LOCK::mutex | 89 | | wait/synch/mutex/sql/LOCK_open | 88 | +---------------------------------------------------+------------+ mysql>SELECT EVENT_NAME, SUM_TIMER_WAITFROM performance_schema.events_waits_summary_global_by_event_nameORDER BY SUM_TIMER_WAIT DESC LIMIT 10;+----------------------------------------+----------------+ | EVENT_NAME | SUM_TIMER_WAIT | +----------------------------------------+----------------+ | wait/io/file/sql/MYSQL_LOG | 1599816582 | | wait/synch/mutex/mysys/THR_LOCK_malloc | 1530083250 | | wait/io/file/sql/binlog_index | 1385291934 | | wait/io/file/sql/FRM | 1292823243 | | wait/io/file/myisam/kfile | 411193611 | | wait/io/file/myisam/dfile | 322401645 | | wait/synch/mutex/mysys/LOCK_alarm | 145126935 | | wait/io/file/sql/casetest | 104324715 | | wait/synch/mutex/sql/LOCK_plugin | 86027823 | | wait/io/file/sql/pid | 72591750 | +----------------------------------------+----------------+
These results show that the THR_LOCK_malloc
mutex is “hot,” both in terms of how often it is used
and amount of time that threads wait attempting to acquire it.
The THR_LOCK_malloc mutex is used only in
debug builds. In production builds it is not hot because it is
nonexistent.
Instance tables document what types of objects are instrumented.
An instrumented object, when used by the server, produces an
event. These tables provide event names and explanatory notes or
status information. For example, the
file_instances table lists instances
of instruments for file I/O operations and their associated files:
mysql>SELECT *FROM performance_schema.file_instances\G*************************** 1. row *************************** FILE_NAME: /opt/mysql-log/60500/binlog.000007 EVENT_NAME: wait/io/file/sql/binlog OPEN_COUNT: 0 *************************** 2. row *************************** FILE_NAME: /opt/mysql/60500/data/mysql/tables_priv.MYI EVENT_NAME: wait/io/file/myisam/kfile OPEN_COUNT: 1 *************************** 3. row *************************** FILE_NAME: /opt/mysql/60500/data/mysql/columns_priv.MYI EVENT_NAME: wait/io/file/myisam/kfile OPEN_COUNT: 1 ...
Setup tables are used to configure and display monitoring
characteristics. For example,
setup_instruments lists the set of
instruments for which events can be collected and shows which of
them are enabled:
mysql> SELECT * FROM performance_schema.setup_instruments;
+---------------------------------------------------+---------+-------+
| NAME | ENABLED | TIMED |
+---------------------------------------------------+---------+-------+
...
| stage/sql/end | NO | NO |
| stage/sql/executing | NO | NO |
| stage/sql/init | NO | NO |
| stage/sql/insert | NO | NO |
...
| statement/sql/load | YES | YES |
| statement/sql/grant | YES | YES |
| statement/sql/check | YES | YES |
| statement/sql/flush | YES | YES |
...
| wait/synch/mutex/sql/LOCK_global_read_lock | YES | YES |
| wait/synch/mutex/sql/LOCK_global_system_variables | YES | YES |
| wait/synch/mutex/sql/LOCK_lock_db | YES | YES |
| wait/synch/mutex/sql/LOCK_manager | YES | YES |
...
| wait/synch/rwlock/sql/LOCK_grant | YES | YES |
| wait/synch/rwlock/sql/LOGGER::LOCK_logger | YES | YES |
| wait/synch/rwlock/sql/LOCK_sys_init_connect | YES | YES |
| wait/synch/rwlock/sql/LOCK_sys_init_slave | YES | YES |
...
| wait/io/file/sql/binlog | YES | YES |
| wait/io/file/sql/binlog_index | YES | YES |
| wait/io/file/sql/casetest | YES | YES |
| wait/io/file/sql/dbopt | YES | YES |
...
To understand how to interpret instrument names, see Section 22.6, “Performance Schema Instrument Naming Conventions”.
To control whether events are collected for an instrument, set its
ENABLED value to YES or
NO. For example:
mysql>UPDATE performance_schema.setup_instrumentsSET ENABLED = 'NO'WHERE NAME = 'wait/synch/mutex/sql/LOCK_mysql_create_db';
The Performance Schema uses collected events to update tables in
the performance_schema database, which act as
“consumers” of event information. The
setup_consumers table lists the
available consumers and which are enabled:
mysql> SELECT * FROM performance_schema.setup_consumers;
+--------------------------------+---------+
| NAME | ENABLED |
+--------------------------------+---------+
| events_stages_current | NO |
| events_stages_history | NO |
| events_stages_history_long | NO |
| events_statements_current | YES |
| events_statements_history | NO |
| events_statements_history_long | NO |
| events_waits_current | NO |
| events_waits_history | NO |
| events_waits_history_long | NO |
| global_instrumentation | YES |
| thread_instrumentation | YES |
| statements_digest | YES |
+--------------------------------+---------+
To control whether the Performance Schema maintains a consumer as
a destination for event information, set its
ENABLED value.
For more information about the setup tables and how to use them to control event collection, see Section 22.4.2, “Performance Schema Event Filtering”.
There are some miscellaneous tables that do not fall into any of
the previous groups. For example,
performance_timers lists the
available event timers and their characteristics. For information
about timers, see Section 22.4.1, “Performance Schema Event Timing”.
For the Performance Schema to be available, it must be configured into the MySQL server at build time. Binary MySQL distributions provided by Oracle Corporation are configured to support the Performance Schema. If you use a binary MySQL distribution from another provider, check with the provider whether the distribution has been appropriately configured.
If you build MySQL from a source distribution, enable the
Performance Schema by running CMake with the
WITH_PERFSCHEMA_STORAGE_ENGINE
option enabled:
shell> cmake . -DWITH_PERFSCHEMA_STORAGE_ENGINE=1
Configuring MySQL with the
-DWITHOUT_PERFSCHEMA_STORAGE_ENGINE=1
option prevents inclusion of the Performance Schema, so if you
want it included, do not use this option. See
Section 2.9.7, “MySQL Source-Configuration Options”.
If you install MySQL over a previous installation that was configured without the Performance Schema (or with an older version of the Performance Schema that has missing or out-of-date tables). One indication of this issue is the presence of messages such as the following in the error log:
[ERROR] Native table 'performance_schema'.'events_waits_history' has the wrong structure [ERROR] Native table 'performance_schema'.'events_waits_history_long' has the wrong structure ...
To correct that problem, perform the MySQL upgrade procedure. See Section 2.11, “Upgrading MySQL”.
To verify whether a server was built with Performance Schema
support, check its help output. If the Performance Schema is
available, the output will mention several variables with names
that begin with performance_schema:
shell> mysqld --verbose --help
...
--performance_schema
Enable the performance schema.
--performance_schema_events_waits_history_long_size=#
Number of rows in events_waits_history_long.
...
You can also connect to the server and look for a line that names
the PERFORMANCE_SCHEMA storage engine
in the output from SHOW ENGINES:
mysql> SHOW ENGINES\G
...
Engine: PERFORMANCE_SCHEMA
Support: YES
Comment: Performance Schema
Transactions: NO
XA: NO
Savepoints: NO
...
If the Performance Schema was not configured into the server at
build time, no row for
PERFORMANCE_SCHEMA will appear in the
output from SHOW ENGINES. You might
see performance_schema listed in the output
from SHOW DATABASES, but it will
have no tables and you will not be able to use it.
A line for PERFORMANCE_SCHEMA in the
SHOW ENGINES output means that the
Performance Schema is available, not that it is enabled. To enable
it, you must do so at server startup, as described in the next
section.
To use the MySQL Performance Schema, it must be enabled at server startup to enable event collection to occur.
Assuming that the Performance Schema is available, it is enabled
by default. To enable or disable it explicitly, start the server
with the performance_schema
variable set to an appropriate value. For example, use these lines
in your my.cnf file:
[mysqld] performance_schema=ON
If the server is unable to allocate any internal buffer during
Performance Schema initialization, the Performance Schema disables
itself and sets
performance_schema to
OFF, and the server runs without
instrumentation.
The Performance Schema also permits instrument and consumer configuration at server startup.
To control an instrument at server startup, use an option of this form:
--performance-schema-instrument='instrument_name=value'
Here, instrument_name is an instrument
name such as wait/synch/mutex/sql/LOCK_open,
and value is one of these values:
OFF, FALSE, or
0: Disable the instrument
ON, TRUE, or
1: Enable and time the instrument
COUNTED: Enable and count (rather than
time) the instrument
Each
--performance-schema-instrument
option can specify only one instrument name, but multiple
instances of the option can be given to configure multiple
instruments. In addition, patterns are permitted in instrument
names to configure instruments that match the pattern. To
configure all condition synchronization instruments as enabled and
counted, use this option:
--performance-schema-instrument='wait/synch/cond/%=COUNTED'
To disable all instruments, use this option:
--performance-schema-instrument='%=OFF'
Longer instrument name strings take precedence over shorter pattern names, regardless of order. For information about specifying patterns to select instruments, see Section 22.4.9, “Naming Instruments or Consumers for Filtering Operations”.
An unrecognized instrument name is ignored. It is possible that a plugin installed later may create the instrument, at which time the name is recognized and configured.
To control a consumer at server startup, use an option of this form:
--performance-schema-consumer-consumer_name=value
Here, consumer_name is a consumer name
such as events_waits_history, and
value is one of these values:
OFF, FALSE, or
0: Do not collect events for the consumer
ON, TRUE, or
1: Collect events for the consumer
For example, to enable the events_waits_history
consumer, use this option:
--performance-schema-consumer-events-waits-history=ON
The permitted consumer names can be found by examining the
setup_consumers table. Patterns are
not permitted. Consumer names in the
setup_consumers table use
underscores, but for consumers set at startup, dashes and
underscores within the name are equivalent.
The Performance Schema includes several system variables that provide configuration information:
mysql> SHOW VARIABLES LIKE 'perf%';
+--------------------------------------------------------+---------+
| Variable_name | Value |
+--------------------------------------------------------+---------+
| performance_schema | ON |
| performance_schema_accounts_size | 100 |
| performance_schema_digests_size | 200 |
| performance_schema_events_stages_history_long_size | 10000 |
| performance_schema_events_stages_history_size | 10 |
| performance_schema_events_statements_history_long_size | 10000 |
| performance_schema_events_statements_history_size | 10 |
| performance_schema_events_waits_history_long_size | 10000 |
| performance_schema_events_waits_history_size | 10 |
| performance_schema_hosts_size | 100 |
| performance_schema_max_cond_classes | 80 |
| performance_schema_max_cond_instances | 1000 |
...
The performance_schema variable
is ON or OFF to indicate
whether the Performance Schema is enabled or disabled. The other
variables indicate table sizes (number of rows) or memory
allocation values.
With the Performance Schema enabled, the number of Performance Schema instances affects the server memory footprint, perhaps to a large extent. It may be necessary to tune the values of Performance Schema system variables to find the number of instances that balances insufficient instrumentation against excessive memory consumption.
To change the value of Performance Schema system variables, set
them at server startup. For example, put the following lines in a
my.cnf file to change the sizes of the
history tables for wait events:
[mysqld] performance_schema performance_schema_events_waits_history_size=20 performance_schema_events_waits_history_long_size=15000
The Performance Schema automatically sizes the values of several of its parameters at server startup if they are not set explicitly. For example, it sizes the parameters that control the sizes of the events waits tables this way. To see which parameters are autosized under this policy, use mysqld --verbose --help and look for those with a default value of −1, or see Section 22.15, “Performance Schema System Variables”.
For each autosized parameter that is not set at server startup, the Performance Schema determines how to set its value based on the value of the following system values, which are considered as “hints” about how you have configured your MySQL server:
max_connections open_files_limit table_definition_cache table_open_cache
To override autosizing for a given parameter, set it to a value other than −1 at startup. In this case, the Performance Schema assigns it the specified value.
At runtime, SHOW VARIABLES displays
the actual values that autosized parameters were set to.
If the Performance Schema is disabled, its autosized parameters
remain set to −1 and SHOW
VARIABLES displays −1.
Specific Performance Schema features can be enabled at runtime to control which types of event collection occur.
Performance Schema setup tables contain information about monitoring configuration:
mysql>SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLESWHERE TABLE_SCHEMA = 'performance_schema'AND TABLE_NAME LIKE 'setup%';+-------------------+ | TABLE_NAME | +-------------------+ | setup_actors | | setup_consumers | | setup_instruments | | setup_objects | | setup_timers | +-------------------+
You can examine the contents of these tables to obtain information
about Performance Schema monitoring characteristics. If you have
the UPDATE privilege, you can
change Performance Schema operation by modifying setup tables to
affect how monitoring occurs. For additional details about these
tables, see Section 22.12.2, “Performance Schema Setup Tables”.
To see which event timers are selected, query the
setup_timers tables:
mysql> SELECT * FROM performance_schema.setup_timers;
+-----------+-------------+
| NAME | TIMER_NAME |
+-----------+-------------+
| idle | MICROSECOND |
| wait | CYCLE |
| stage | NANOSECOND |
| statement | NANOSECOND |
+-----------+-------------+
The NAME value indicates the type of instrument
to which the timer applies, and TIMER_NAME
indicates which timer applies to those instruments. The timer
applies to instruments where their name begins with a component
matching the NAME value.
To change the timer, update the NAME value. For
example, to use the NANOSECOND timer for the
wait timer:
mysql>UPDATE performance_schema.setup_timersSET TIMER_NAME = 'NANOSECOND'WHERE NAME = 'wait';mysql>SELECT * FROM performance_schema.setup_timers;+-----------+-------------+ | NAME | TIMER_NAME | +-----------+-------------+ | idle | MICROSECOND | | wait | NANOSECOND | | stage | NANOSECOND | | statement | NANOSECOND | +-----------+-------------+
For discussion of timers, see Section 22.4.1, “Performance Schema Event Timing”.
The setup_instruments and
setup_consumers tables list the
instruments for which events can be collected and the types of
consumers for which event information actually is collected,
respectively. Other setup tables enable further modification of
the monitoring configuration.
Section 22.4.2, “Performance Schema Event Filtering”, discusses how you
can modify these tables to affect event collection.
If there are Performance Schema configuration changes that must be
made at runtime using SQL statements and you would like these
changes to take effect each time the server starts, put the
statements in a file and start the server with the
init_file system variable set to
name the file. This strategy can also be useful if you have
multiple monitoring configurations, each tailored to produce a
different kind of monitoring, such as casual server health
monitoring, incident investigation, application behavior
troubleshooting, and so forth. Put the statements for each
monitoring configuration into their own file and specify the
appropriate file as the init_file
value when you start the server.
Events are collected by means of instrumentation added to the server source code. Instruments time events, which is how the Performance Schema provides an idea of how long events take. It is also possible to configure instruments not to collect timing information. This section discusses the available timers and their characteristics, and how timing values are represented in events.
Two Performance Schema tables provide timer information:
performance_timers lists the
available timers and their characteristics.
setup_timers indicates which
timers are used for which instruments.
Each timer row in setup_timers
must refer to one of the timers listed in
performance_timers.
Timers vary in precision and amount of overhead. To see what
timers are available and their characteristics, check the
performance_timers table:
mysql> SELECT * FROM performance_schema.performance_timers;
+-------------+-----------------+------------------+----------------+
| TIMER_NAME | TIMER_FREQUENCY | TIMER_RESOLUTION | TIMER_OVERHEAD |
+-------------+-----------------+------------------+----------------+
| CYCLE | 2389029850 | 1 | 72 |
| NANOSECOND | 1000000000 | 1 | 112 |
| MICROSECOND | 1000000 | 1 | 136 |
| MILLISECOND | 1036 | 1 | 168 |
| TICK | 105 | 1 | 2416 |
+-------------+-----------------+------------------+----------------+
If the values associated with a given timer name are
NULL, that timer is not supported on your
platform. The rows that do not contain NULL
indicate which timers you can use in
setup_timers.
The columns have these meanings:
The TIMER_NAME column shows the names
of the available timers. CYCLE refers
to the timer that is based on the CPU (processor) cycle
counter. The timers in
setup_timers that you can use
are those that do not have NULL in the
other columns. If the values associated with a given timer
name are NULL, that timer is not
supported on your platform.
TIMER_FREQUENCY indicates the number of
timer units per second. For a cycle timer, the frequency
is generally related to the CPU speed. The value shown was
obtained on a system with a 2.4GHz processor. The other
timers are based on fixed fractions of seconds. For
TICK, the frequency may vary by
platform (for example, some use 100 ticks/second, others
1000 ticks/second).
TIMER_RESOLUTION indicates the number
of timer units by which timer values increase at a time.
If a timer has a resolution of 10, its value increases by
10 each time.
TIMER_OVERHEAD is the minimal number of
cycles of overhead to obtain one timing with the given
timer. The overhead per event is twice the value displayed
because the timer is invoked at the beginning and end of
the event.
To see which timers are in effect or to change timers, access
the setup_timers table:
mysql>SELECT * FROM performance_schema.setup_timers;+-----------+-------------+ | NAME | TIMER_NAME | +-----------+-------------+ | idle | MICROSECOND | | wait | CYCLE | | stage | NANOSECOND | | statement | NANOSECOND | +-----------+-------------+ mysql>UPDATE performance_schema.setup_timersSET TIMER_NAME = 'MICROSECOND'WHERE NAME = 'idle';mysql>SELECT * FROM performance_schema.setup_timers;+-----------+-------------+ | NAME | TIMER_NAME | +-----------+-------------+ | idle | MICROSECOND | | wait | CYCLE | | stage | NANOSECOND | | statement | NANOSECOND | +-----------+-------------+
By default, the Performance Schema uses the best timer available for each instrument type, but you can select a different one.
To time wait events, the most important criterion is to reduce
overhead, at the possible expense of the timer accuracy, so
using the CYCLE timer is the best.
The time a statement (or stage) takes to execute is in general
orders of magnitude larger than the time it takes to execute a
single wait. To time statements, the most important criterion
is to have an accurate measure, which is not affected by
changes in processor frequency, so using a timer which is not
based on cycles is the best. The default timer for statements
is NANOSECOND. The extra
“overhead” compared to the
CYCLE timer is not significant, because the
overhead caused by calling a timer twice (once when the
statement starts, once when it ends) is orders of magnitude
less compared to the CPU time used to execute the statement
itself. Using the CYCLE timer has no
benefit here, only drawbacks.
The precision offered by the cycle counter depends on
processor speed. If the processor runs at 1 GHz (one billion
cycles/second) or higher, the cycle counter delivers
sub-nanosecond precision. Using the cycle counter is much
cheaper than getting the actual time of day. For example, the
standard gettimeofday() function can take
hundreds of cycles, which is an unacceptable overhead for data
gathering that may occur thousands or millions of times per
second.
Cycle counters also have disadvantages:
End users expect to see timings in wall-clock units, such as fractions of a second. Converting from cycles to fractions of seconds can be expensive. For this reason, the conversion is a quick and fairly rough multiplication operation.
Processor cycle rate might change, such as when a laptop goes into power-saving mode or when a CPU slows down to reduce heat generation. If a processor's cycle rate fluctuates, conversion from cycles to real-time units is subject to error.
Cycle counters might be unreliable or unavailable
depending on the processor or the operating system. For
example, on Pentiums, the instruction is
RDTSC (an assembly-language rather than
a C instruction) and it is theoretically possible for the
operating system to prevent user-mode programs from using
it.
Some processor details related to out-of-order execution or multiprocessor synchronization might cause the counter to seem fast or slow by up to 1000 cycles.
MySQL works with cycle counters on x386 (Windows, macOS, Linux, Solaris, and other Unix flavors), PowerPC, and IA-64.
Rows in Performance Schema tables that store current events
and historical events have three columns to represent timing
information: TIMER_START and
TIMER_END indicate when an event started
and finished, and TIMER_WAIT indicates
event duration.
The setup_instruments table has
an ENABLED column to indicate the
instruments for which to collect events. The table also has a
TIMED column to indicate which instruments
are timed. If an instrument is not enabled, it produces no
events. If an enabled instrument is not timed, events produced
by the instrument have NULL for the
TIMER_START, TIMER_END,
and TIMER_WAIT timer values. This in turn
causes those values to be ignored when calculating aggregate
time values in summary tables (sum, minimum, maximum, and
average).
Internally, times within events are stored in units given by the timer in effect when event timing begins. For display when events are retrieved from Performance Schema tables, times are shown in picoseconds (trillionths of a second) to normalize them to a standard unit, regardless of which timer is selected.
Modifications to the setup_timers
table affect monitoring immediately. Events already in
progress may use the original timer for the begin time and the
new timer for the end time. To avoid unpredictable results
after you make timer changes, use
TRUNCATE TABLE to reset
Performance Schema statistics.
The timer baseline (“time zero”) occurs at
Performance Schema initialization during server startup.
TIMER_START and
TIMER_END values in events represent
picoseconds since the baseline. TIMER_WAIT
values are durations in picoseconds.
Picosecond values in events are approximate. Their accuracy is
subject to the usual forms of error associated with conversion
from one unit to another. If the CYCLE
timer is used and the processor rate varies, there might be
drift. For these reasons, it is not reasonable to look at the
TIMER_START value for an event as an
accurate measure of time elapsed since server startup. On the
other hand, it is reasonable to use
TIMER_START or
TIMER_WAIT values in ORDER
BY clauses to order events by start time or
duration.
The choice of picoseconds in events rather than a value such
as microseconds has a performance basis. One implementation
goal was to show results in a uniform time unit, regardless of
the timer. In an ideal world this time unit would look like a
wall-clock unit and be reasonably precise; in other words,
microseconds. But to convert cycles or nanoseconds to
microseconds, it would be necessary to perform a division for
every instrumentation. Division is expensive on many
platforms. Multiplication is not expensive, so that is what is
used. Therefore, the time unit is an integer multiple of the
highest possible TIMER_FREQUENCY value,
using a multiplier large enough to ensure that there is no
major precision loss. The result is that the time unit is
“picoseconds.” This precision is spurious, but
the decision enables overhead to be minimized.
Before MySQL 5.6.26, while a wait, stage, or statement event
is executing, the respective current-event tables display the
event with TIMER_START populated, but with
TIMER_END and TIMER_WAIT
set to NULL:
events_waits_current events_stages_current events_statements_current
As of MySQL 5.6.26, current-event timing provides more information. To make it possible to determine how long a not-yet-completed event has been running, the timer columns are set as follows:
TIMER_START is populated.
TIMER_END is populated with the current
timer value.
TIMER_WAIT is populated with the time
elapsed so far (TIMER_END −
TIMER_START).
Events that have not yet completed have an
END_EVENT_ID value of
NULL. To assess time elapsed so far for an
event, use the TIMER_WAIT column.
Therefore, to identify events that have not yet completed and
have taken longer than N
picoseconds thus far, monitoring applications can use this
expression in queries:
WHERE END_EVENT_ID IS NULL AND TIMER_WAIT > N
Event identification as just described assumes that the
corresponding instruments have ENABLED and
TIMED set to YES and
that the relevant consumers are enabled.
Events are processed in a producer/consumer fashion:
Instrumented code is the source for events and produces
events to be collected. The
setup_instruments table lists
the instruments for which events can be collected, whether
they are enabled, and (for enabled instruments) whether to
collect timing information:
mysql> SELECT * FROM performance_schema.setup_instruments;
+---------------------------------------------------+---------+-------+
| NAME | ENABLED | TIMED |
+---------------------------------------------------+---------+-------+
...
| wait/synch/mutex/sql/LOCK_global_read_lock | YES | YES |
| wait/synch/mutex/sql/LOCK_global_system_variables | YES | YES |
| wait/synch/mutex/sql/LOCK_lock_db | YES | YES |
| wait/synch/mutex/sql/LOCK_manager | YES | YES |
...
The setup_instruments table
provides the most basic form of control over event
production. To further refine event production based on the
type of object or thread being monitored, other tables may
be used as described in
Section 22.4.3, “Event Pre-Filtering”.
Performance Schema tables are the destinations for events
and consume events. The
setup_consumers table lists the
types of consumers to which event information can be sent
and whether they are enabled:
mysql> SELECT * FROM performance_schema.setup_consumers;
+--------------------------------+---------+
| NAME | ENABLED |
+--------------------------------+---------+
| events_stages_current | NO |
| events_stages_history | NO |
| events_stages_history_long | NO |
| events_statements_current | YES |
| events_statements_history | NO |
| events_statements_history_long | NO |
| events_waits_current | NO |
| events_waits_history | NO |
| events_waits_history_long | NO |
| global_instrumentation | YES |
| thread_instrumentation | YES |
| statements_digest | YES |
+--------------------------------+---------+
Filtering can be done at different stages of performance monitoring:
Pre-filtering. This is done by modifying Performance Schema configuration so that only certain types of events are collected from producers, and collected events update only certain consumers. To do this, enable or disable instruments or consumers. Pre-filtering is done by the Performance Schema and has a global effect that applies to all users.
Reasons to use pre-filtering:
To reduce overhead. Performance Schema overhead should be minimal even with all instruments enabled, but perhaps you want to reduce it further. Or you do not care about timing events and want to disable the timing code to eliminate timing overhead.
To avoid filling the current-events or history tables with events in which you have no interest. Pre-filtering leaves more “room” in these tables for instances of rows for enabled instrument types. If you enable only file instruments with pre-filtering, no rows are collected for nonfile instruments. With post-filtering, nonfile events are collected, leaving fewer rows for file events.
To avoid maintaining some kinds of event tables. If you disable a consumer, the server does not spend time maintaining destinations for that consumer. For example, if you do not care about event histories, you can disable the history table consumers to improve performance.
Post-filtering.
This involves the use of WHERE clauses
in queries that select information from Performance Schema
tables, to specify which of the available events you want
to see. Post-filtering is performed on a per-user basis
because individual users select which of the available
events are of interest.
Reasons to use post-filtering:
To avoid making decisions for individual users about which event information is of interest.
To use the Performance Schema to investigate a performance issue when the restrictions to impose using pre-filtering are not known in advance.
The following sections provide more detail about pre-filtering and provide guidelines for naming instruments or consumers in filtering operations. For information about writing queries to retrieve information (post-filtering), see Section 22.5, “Performance Schema Queries”.
Pre-filtering is done by the Performance Schema and has a global effect that applies to all users. Pre-filtering can be applied to either the producer or consumer stage of event processing:
To configure pre-filtering at the producer stage, several tables can be used:
setup_instruments indicates
which instruments are available. An instrument disabled
in this table produces no events regardless of the
contents of the other production-related setup tables.
An instrument enabled in this table is permitted to
produce events, subject to the contents of the other
tables.
setup_objects controls
whether the Performance Schema monitors particular table
objects.
threads indicates whether
monitoring is enabled for each server thread.
setup_actors determines the
initial monitoring state for new foreground threads.
To configure pre-filtering at the consumer stage, modify the
setup_consumers table. This
determines the destinations to which events are sent.
setup_consumers also implicitly
affects event production. If a given event will not be sent
to any destination (that is, will not be consumed), the
Performance Schema does not produce it.
Modifications to any of these tables affect monitoring immediately, with some exceptions:
Modifications to some instruments in the
setup_instruments table are
effective only at server startup; changing them at runtime
has no effect. This affects primarily mutexes, conditions,
and rwlocks in the server, although there may be other
instruments for which this is true.
Modifications to the
setup_actors table affect only
foreground threads created subsequent to the modification,
not existing threads.
When you change the monitoring configuration, the Performance
Schema does not flush the history tables. Events already
collected remain in the current-events and history tables until
displaced by newer events. If you disable instruments, you might
need to wait a while before events for them are displaced by
newer events of interest. Alternatively, use
TRUNCATE TABLE to empty the
history tables.
After making instrumentation changes, you might want to truncate
the summary tables. Generally, the effect is to reset the
summary columns to 0 or NULL, not to remove
rows. This enables you to clear collected values and restart
aggregation. That might be useful, for example, after you have
made a runtime configuration change. Exceptions to this
truncation behavior are noted in individual summary table
sections.
The following sections describe how to use specific tables to control Performance Schema pre-filtering.
The setup_instruments table lists
the available instruments:
mysql> SELECT * FROM performance_schema.setup_instruments;
+---------------------------------------------------+---------+-------+
| NAME | ENABLED | TIMED |
+---------------------------------------------------+---------+-------+
...
| stage/sql/end | NO | NO |
| stage/sql/executing | NO | NO |
| stage/sql/init | NO | NO |
| stage/sql/insert | NO | NO |
...
| statement/sql/load | YES | YES |
| statement/sql/grant | YES | YES |
| statement/sql/check | YES | YES |
| statement/sql/flush | YES | YES |
...
| wait/synch/mutex/sql/LOCK_global_read_lock | YES | YES |
| wait/synch/mutex/sql/LOCK_global_system_variables | YES | YES |
| wait/synch/mutex/sql/LOCK_lock_db | YES | YES |
| wait/synch/mutex/sql/LOCK_manager | YES | YES |
...
| wait/synch/rwlock/sql/LOCK_grant | YES | YES |
| wait/synch/rwlock/sql/LOGGER::LOCK_logger | YES | YES |
| wait/synch/rwlock/sql/LOCK_sys_init_connect | YES | YES |
| wait/synch/rwlock/sql/LOCK_sys_init_slave | YES | YES |
...
| wait/io/file/sql/binlog | YES | YES |
| wait/io/file/sql/binlog_index | YES | YES |
| wait/io/file/sql/casetest | YES | YES |
| wait/io/file/sql/dbopt | YES | YES |
...
To control whether an instrument is enabled, set its
ENABLED column to YES or
NO. To configure whether to collect timing
information for an enabled instrument, set its
TIMED value to YES or
NO. Setting the TIMED
column affects Performance Schema table contents as described in
Section 22.4.1, “Performance Schema Event Timing”.
Modifications to most
setup_instruments rows affect
monitoring immediately. For some instruments, modifications are
effective only at server startup; changing them at runtime has
no effect. This affects primarily mutexes, conditions, and
rwlocks in the server, although there may be other instruments
for which this is true.
The setup_instruments table
provides the most basic form of control over event production.
To further refine event production based on the type of object
or thread being monitored, other tables may be used as described
in Section 22.4.3, “Event Pre-Filtering”.
The following examples demonstrate possible operations on the
setup_instruments table. These
changes, like other pre-filtering operations, affect all users.
Some of these queries use the LIKE
operator and a pattern match instrument names. For additional
information about specifying patterns to select instruments, see
Section 22.4.9, “Naming Instruments or Consumers for Filtering Operations”.
Disable all instruments:
UPDATE performance_schema.setup_instruments SET ENABLED = 'NO';
Now no events will be collected.
Disable all file instruments, adding them to the current set of disabled instruments:
UPDATE performance_schema.setup_instruments SET ENABLED = 'NO' WHERE NAME LIKE 'wait/io/file/%';
Disable only file instruments, enable all other instruments:
UPDATE performance_schema.setup_instruments SET ENABLED = IF(NAME LIKE 'wait/io/file/%', 'NO', 'YES');
Enable all but those instruments in the
mysys library:
UPDATE performance_schema.setup_instruments SET ENABLED = CASE WHEN NAME LIKE '%/mysys/%' THEN 'YES' ELSE 'NO' END;
Disable a specific instrument:
UPDATE performance_schema.setup_instruments SET ENABLED = 'NO' WHERE NAME = 'wait/synch/mutex/mysys/TMPDIR_mutex';
To toggle the state of an instrument, “flip”
its ENABLED value:
UPDATE performance_schema.setup_instruments SET ENABLED = IF(ENABLED = 'YES', 'NO', 'YES') WHERE NAME = 'wait/synch/mutex/mysys/TMPDIR_mutex';
Disable timing for all events:
UPDATE performance_schema.setup_instruments SET TIMED = 'NO';
The setup_objects table controls
whether the Performance Schema monitors particular table
objects. The initial setup_objects
contents look like this:
mysql> SELECT * FROM performance_schema.setup_objects;
+-------------+--------------------+-------------+---------+-------+
| OBJECT_TYPE | OBJECT_SCHEMA | OBJECT_NAME | ENABLED | TIMED |
+-------------+--------------------+-------------+---------+-------+
| TABLE | mysql | % | NO | NO |
| TABLE | performance_schema | % | NO | NO |
| TABLE | information_schema | % | NO | NO |
| TABLE | % | % | YES | YES |
+-------------+--------------------+-------------+---------+-------+
Modifications to the setup_objects
table affect object monitoring immediately.
The OBJECT_TYPE column indicates the type of
object to which a row applies. TABLE
filtering affects table I/O events
(wait/io/table/sql/handler instrument) and
table lock events
(wait/lock/table/sql/handler instrument).
The OBJECT_SCHEMA and
OBJECT_NAME columns should contain a literal
schema or table name, or '%' to match any
name.
The ENABLED column indicates whether matching
objects are monitored, and TIMED indicates
whether to collect timing information. Setting the
TIMED column affects Performance Schema table
contents as described in
Section 22.4.1, “Performance Schema Event Timing”.
The effect of the default object configuration is to instrument
all tables except those in the mysql,
INFORMATION_SCHEMA, and
performance_schema databases. (Tables in the
INFORMATION_SCHEMA database are not
instrumented regardless of the contents of
setup_objects; the row for
information_schema.% simply makes this
default explicit.)
When the Performance Schema checks for a match in
setup_objects, it tries to find
more specific matches first. For rows that match a given
OBJECT_TYPE, the Performance Schema checks
rows in this order:
Rows with
OBJECT_SCHEMA='
and
literal'OBJECT_NAME='.
literal'
Rows with
OBJECT_SCHEMA='
and literal'OBJECT_NAME='%'.
Rows with OBJECT_SCHEMA='%' and
OBJECT_NAME='%'.
For example, with a table db1.t1, the
Performance Schema looks in TABLE rows for a
match for 'db1' and 't1',
then for 'db1' and '%',
then for '%' and '%'. The
order in which matching occurs matters because different
matching setup_objects rows can
have different ENABLED and
TIMED values.
For table-related events, the Performance Schema combines the
contents of setup_objects with
setup_instruments to determine
whether to enable instruments and whether to time enabled
instruments:
For tables that match a row in
setup_objects, table
instruments produce events only if
ENABLED is YES in both
setup_instruments and
setup_objects.
The TIMED values in the two tables are
combined, so that timing information is collected only when
both values are YES.
Suppose that setup_objects contains
the following TABLE rows that apply to
db1, db2, and
db3:
+-------------+---------------+-------------+---------+-------+ | OBJECT_TYPE | OBJECT_SCHEMA | OBJECT_NAME | ENABLED | TIMED | +-------------+---------------+-------------+---------+-------+ | TABLE | db1 | t1 | YES | YES | | TABLE | db1 | t2 | NO | NO | | TABLE | db2 | % | YES | YES | | TABLE | db3 | % | NO | NO | | TABLE | % | % | YES | YES | +-------------+---------------+-------------+---------+-------+
If a table-related instrument in
setup_instruments has an
ENABLED value of NO,
events for the object are not monitored. If the
ENABLED value is YES,
event monitoring occurs according to the
ENABLED value in the relevant
setup_objects row:
db1.t1 events are monitored
db1.t2 events are not monitored
db2.t3 events are monitored
db3.t4 events are not monitored
db4.t5 events are monitored
Similar logic applies for combining the TIMED
columns from the setup_instruments
and setup_objects tables to
determine whether to collect event timing information.
If a persistent table and a temporary table have the same name,
matching against setup_objects rows
occurs the same way for both. It is not possible to enable
monitoring for one table but not the other. However, each table
is instrumented separately.
The threads table contains a row
for each server thread. Each row contains information about a
thread and indicates whether monitoring is enabled for it. For
the Performance Schema to monitor a thread, these things must be
true:
The thread_instrumentation consumer in
the setup_consumers table must
be YES.
The threads.INSTRUMENTED column must be
YES.
Monitoring occurs only for those thread events produced from
instruments that are enabled in the
setup_instruments table.
The INSTRUMENTED column in the
threads table indicates the
monitoring state for each thread. For foreground threads
(resulting from client connections), the initial
INSTRUMENTED value is determined by whether
the user account associated with the thread matches any row in
the setup_actors table.
For background threads, there is no associated user.
INSTRUMENTED is YES by
default and setup_actors is not
consulted.
The initial setup_actors contents
look like this:
mysql> SELECT * FROM performance_schema.setup_actors;
+------+------+------+
| HOST | USER | ROLE |
+------+------+------+
| % | % | % |
+------+------+------+
The HOST and USER columns
should contain a literal host or user name, or
'%' to match any name.
The Performance Schema uses the HOST and
USER columns to match each new foreground
thread. (ROLE is unused.) The
INSTRUMENTED value for the thread becomes
YES if any row matches, NO
otherwise. This enables instrumenting to be applied selectively
per host, user, or combination of host and user.
By default, monitoring is enabled for all new foreground threads
because the setup_actors table
initially contains a row with '%' for both
HOST and USER. To perform
more limited matching such as to enable monitoring only for some
foreground threads, you must delete this row because it matches
any connection.
Suppose that you modify
setup_actors as follows:
TRUNCATE TABLE performance_schema.setup_actors;
Now setup_actors is empty and there are no
rows that could match incoming connections. Consequently, the
Performance Schema sets the INSTRUMENTED
column to NO for all new foreground threads.
Suppose that you further modify
setup_actors:
INSERT INTO performance_schema.setup_actors
(HOST,USER,ROLE) VALUES('localhost','joe','%');
INSERT INTO performance_schema.setup_actors
(HOST,USER,ROLE) VALUES('%','sam','%');
Now the Performance Schema determines how to set the
INSTRUMENTED value for new connection threads
as follows:
If joe connects from the local host, the
connection matches the first inserted row.
If joe connects from any other host,
there is no match.
If sam connects from any host, the
connection matches the second inserted row.
For any other connection, there is no match.
Modifications to the setup_actors
table affect only foreground threads created subsequent to the
modification, not existing threads. To affect existing threads,
modify the INSTRUMENTED column of
threads table rows.
The setup_consumers table lists the
available consumer types and which are enabled:
mysql> SELECT * FROM performance_schema.setup_consumers;
+--------------------------------+---------+
| NAME | ENABLED |
+--------------------------------+---------+
| events_stages_current | NO |
| events_stages_history | NO |
| events_stages_history_long | NO |
| events_statements_current | YES |
| events_statements_history | NO |
| events_statements_history_long | NO |
| events_waits_current | NO |
| events_waits_history | NO |
| events_waits_history_long | NO |
| global_instrumentation | YES |
| thread_instrumentation | YES |
| statements_digest | YES |
+--------------------------------+---------+
Modify the setup_consumers table to
affect pre-filtering at the consumer stage and determine the
destinations to which events are sent. To enable or disable a
consumer, set its ENABLED value to
YES or NO.
Modifications to the
setup_consumers table affect
monitoring immediately.
If you disable a consumer, the server does not spend time maintaining destinations for that consumer. For example, if you do not care about historical event information, disable the history consumers:
UPDATE performance_schema.setup_consumers SET ENABLED = 'NO' WHERE NAME LIKE '%history%';
The consumer settings in the
setup_consumers table form a
hierarchy from higher levels to lower. The following principles
apply:
Destinations associated with a consumer receive no events unless the Performance Schema checks the consumer and the consumer is enabled.
A consumer is checked only if all consumers it depends on (if any) are enabled.
If a consumer is not checked, or is checked but is disabled, other consumers that depend on it are not checked.
Dependent consumers may have their own dependent consumers.
If an event would not be sent to any destination, the Performance Schema does not produce it.
The following lists describe the available consumer values. For discussion of several representative consumer configurations and their effect on instrumentation, see Section 22.4.8, “Example Consumer Configurations”.
global_instrumentation is the highest
level consumer. If
global_instrumentation is
NO, it disables global instrumentation.
All other settings are lower level and are not checked; it
does not matter what they are set to. No global or per
thread information is maintained and no individual events
are collected in the current-events or event-history
tables. If global_instrumentation is
YES, the Performance Schema maintains
information for global states and also checks the
thread_instrumentation consumer.
thread_instrumentation is checked only
if global_instrumentation is
YES. Otherwise, if
thread_instrumentation is
NO, it disables thread-specific
instrumentation and all lower-level settings are ignored.
No information is maintained per thread and no individual
events are collected in the current-events or
event-history tables. If
thread_instrumentation is
YES, the Performance Schema maintains
thread-specific information and also checks
events_
consumers.
xxx_current
These consumers require both
global_instrumentation and
thread_instrumentation to be
YES or they are not checked. If checked,
they act as follows:
events_waits_current, if
NO, disables collection of individual
wait events in the
events_waits_current table.
If YES, it enables wait event
collection and the Performance Schema checks the
events_waits_history and
events_waits_history_long consumers.
events_waits_history is not checked if
event_waits_current is
NO. Otherwise, an
events_waits_history value of
NO or YES disables
or enables collection of wait events in the
events_waits_history table.
events_waits_history_long is not
checked if event_waits_current is
NO. Otherwise, an
events_waits_history_long value of
NO or YES disables
or enables collection of wait events in the
events_waits_history_long
table.
These consumers require both
global_instrumentation and
thread_instrumentation to be
YES or they are not checked. If checked,
they act as follows:
events_stages_current, if
NO, disables collection of individual
stage events in the
events_stages_current table.
If YES, it enables stage event
collection and the Performance Schema checks the
events_stages_history and
events_stages_history_long consumers.
events_stages_history is not checked if
event_stages_current is
NO. Otherwise, an
events_stages_history value of
NO or YES disables
or enables collection of stage events in the
events_stages_history table.
events_stages_history_long is not
checked if event_stages_current is
NO. Otherwise, an
events_stages_history_long value of
NO or YES disables
or enables collection of stage events in the
events_stages_history_long
table.
These consumers require both
global_instrumentation and
thread_instrumentation to be
YES or they are not checked. If checked,
they act as follows:
events_statements_current, if
NO, disables collection of individual
statement events in the
events_statements_current
table. If YES, it enables statement
event collection and the Performance Schema checks the
events_statements_history and
events_statements_history_long
consumers.
events_statements_history is not
checked if events_statements_current is
NO. Otherwise, an
events_statements_history value of
NO or YES disables
or enables collection of statement events in the
events_statements_history
table.
events_statements_history_long is not
checked if events_statements_current is
NO. Otherwise, an
events_statements_history_long value of
NO or YES disables
or enables collection of statement events in the
events_statements_history_long
table.
The statements_digest consumer requires
global_instrumentation to be
YES or it is not checked. There is no
dependency on the statement event consumers, so you can obtain
statistics per digest without having to collect statistics in
events_statements_current, which
is advantageous in terms of overhead. Conversely, you can get
detailed statements in
events_statements_current without
digests (the DIGEST and
DIGEST_TEXT columns will be
NULL).
For more information about statement digesting, see Section 22.10, “Performance Schema Statement Digests”.
The consumer settings in the
setup_consumers table form a
hierarchy from higher levels to lower. The following discussion
describes how consumers work, showing specific configurations
and their effects as consumer settings are enabled progressively
from high to low. The consumer values shown are representative.
The general principles described here apply to other consumer
values that may be available.
The configuration descriptions occur in order of increasing functionality and overhead. If you do not need the information provided by enabling lower-level settings, disable them and the Performance Schema will execute less code on your behalf and you will have less information to sift through.
The setup_consumers table contains
the following hierarchy of values:
global_instrumentation
thread_instrumentation
events_waits_current
events_waits_history
events_waits_history_long
events_stages_current
events_stages_history
events_stages_history_long
events_statements_current
events_statements_history
events_statements_history_long
statements_digest
In the consumer hierarchy, the consumers for waits, stages, and statements are all at the same level. This differs from the event nesting hierarchy, for which wait events nest within stage events, which nest within statement events.
If a given consumer setting is NO, the
Performance Schema disables the instrumentation associated with
the consumer and ignores all lower-level settings. If a given
setting is YES, the Performance Schema
enables the instrumentation associated with it and checks the
settings at the next lowest level. For a description of the
rules for each consumer, see
Section 22.4.7, “Pre-Filtering by Consumer”.
For example, if global_instrumentation is
enabled, thread_instrumentation is checked.
If thread_instrumentation is enabled, the
events_
consumers are checked. If of these
xxx_currentevents_waits_current is enabled,
events_waits_history and
events_waits_history_long are checked.
Each of the following configuration descriptions indicates which setup elements the Performance Schema checks and which output tables it maintains (that is, for which tables it collects information).
Server configuration state:
mysql> SELECT * FROM performance_schema.setup_consumers;
+---------------------------+---------+
| NAME | ENABLED |
+---------------------------+---------+
| global_instrumentation | NO |
...
+---------------------------+---------+
In this configuration, nothing is instrumented.
Setup elements checked:
Table setup_consumers,
consumer global_instrumentation
Output tables maintained:
None
Server configuration state:
mysql> SELECT * FROM performance_schema.setup_consumers;
+---------------------------+---------+
| NAME | ENABLED |
+---------------------------+---------+
| global_instrumentation | YES |
| thread_instrumentation | NO |
...
+---------------------------+---------+
In this configuration, instrumentation is maintained only for global states. Per-thread instrumentation is disabled.
Additional setup elements checked, relative to the preceding configuration:
Table setup_consumers,
consumer thread_instrumentation
Table setup_instruments
Table setup_objects
Table setup_timers
Additional output tables maintained, relative to the preceding configuration:
Server configuration state:
mysql> SELECT * FROM performance_schema.setup_consumers;
+--------------------------------+---------+
| NAME | ENABLED |
+--------------------------------+---------+
| global_instrumentation | YES |
| thread_instrumentation | YES |
| events_waits_current | NO |
...
| events_stages_current | NO |
...
| events_statements_current | YES |
...
+--------------------------------+---------+
In this configuration, instrumentation is maintained globally and per thread. No individual events are collected in the current-events or event-history tables.
Additional setup elements checked, relative to the preceding configuration:
Table setup_consumers,
consumers
events_,
where xxx_currentxxx is
waits, stages,
statements
Table setup_actors
Column threads.instrumented
Additional output tables maintained, relative to the preceding configuration:
events_,
where xxx_summary_by_yyy_by_event_namexxx is
waits, stages,
statements; and
yyy is
thread, user,
host, account
Server configuration state:
mysql> SELECT * FROM performance_schema.setup_consumers;
+--------------------------------+---------+
| NAME | ENABLED |
+--------------------------------+---------+
| global_instrumentation | YES |
| thread_instrumentation | YES |
| events_waits_current | YES |
| events_waits_history | NO |
| events_waits_history_long | NO |
| events_stages_current | YES |
| events_stages_history | NO |
| events_stages_history_long | NO |
| events_statements_current | YES |
| events_statements_history | NO |
| events_statements_history_long | NO |
...
+--------------------------------+---------+
In this configuration, instrumentation is maintained globally and per thread. Individual events are collected in the current-events table, but not in the event-history tables.
Additional setup elements checked, relative to the preceding configuration:
Consumers
events_,
where xxx_historyxxx is
waits, stages,
statements
Consumers
events_,
where xxx_history_longxxx is
waits, stages,
statements
Additional output tables maintained, relative to the preceding configuration:
events_,
where xxx_currentxxx is
waits, stages,
statements
The preceding configuration collects no event history because
the
events_
and
xxx_historyevents_
consumers are disabled. Those consumers can be enabled
separately or together to collect event history per thread,
globally, or both.
xxx_history_long
This configuration collects event history per thread, but not globally:
mysql> SELECT * FROM performance_schema.setup_consumers;
+--------------------------------+---------+
| NAME | ENABLED |
+--------------------------------+---------+
| global_instrumentation | YES |
| thread_instrumentation | YES |
| events_waits_current | YES |
| events_waits_history | YES |
| events_waits_history_long | NO |
| events_stages_current | YES |
| events_stages_history | YES |
| events_stages_history_long | NO |
| events_statements_current | YES |
| events_statements_history | YES |
| events_statements_history_long | NO |
...
+--------------------------------+---------+
Event-history tables maintained for this configuration:
events_,
where xxx_historyxxx is
waits, stages,
statements
This configuration collects event history globally, but not per thread:
mysql> SELECT * FROM performance_schema.setup_consumers;
+--------------------------------+---------+
| NAME | ENABLED |
+--------------------------------+---------+
| global_instrumentation | YES |
| thread_instrumentation | YES |
| events_waits_current | YES |
| events_waits_history | NO |
| events_waits_history_long | YES |
| events_stages_current | YES |
| events_stages_history | NO |
| events_stages_history_long | YES |
| events_statements_current | YES |
| events_statements_history | NO |
| events_statements_history_long | YES |
...
+--------------------------------+---------+
Event-history tables maintained for this configuration:
events_,
where xxx_history_longxxx is
waits, stages,
statements
This configuration collects event history per thread and globally:
mysql> SELECT * FROM performance_schema.setup_consumers;
+--------------------------------+---------+
| NAME | ENABLED |
+--------------------------------+---------+
| global_instrumentation | YES |
| thread_instrumentation | YES |
| events_waits_current | YES |
| events_waits_history | YES |
| events_waits_history_long | YES |
| events_stages_current | YES |
| events_stages_history | YES |
| events_stages_history_long | YES |
| events_statements_current | YES |
| events_statements_history | YES |
| events_statements_history_long | YES |
...
+--------------------------------+---------+
Event-history tables maintained for this configuration:
events_,
where xxx_historyxxx is
waits, stages,
statements
events_,
where xxx_history_longxxx is
waits, stages,
statements
Names given for filtering operations can be as specific or general as required. To indicate a single instrument or consumer, specify its name in full:
UPDATE performance_schema.setup_instruments SET ENABLED = 'NO' WHERE NAME = 'wait/synch/mutex/myisammrg/MYRG_INFO::mutex'; UPDATE performance_schema.setup_consumers SET ENABLED = 'NO' WHERE NAME = 'events_waits_current';
To specify a group of instruments or consumers, use a pattern that matches the group members:
UPDATE performance_schema.setup_instruments SET ENABLED = 'NO' WHERE NAME LIKE 'wait/synch/mutex/%'; UPDATE performance_schema.setup_consumers SET ENABLED = 'NO' WHERE NAME LIKE '%history%';
If you use a pattern, it should be chosen so that it matches all the items of interest and no others. For example, to select all file I/O instruments, it is better to use a pattern that includes the entire instrument name prefix:
... WHERE NAME LIKE 'wait/io/file/%';
A pattern of '%/file/%' will match other
instruments that have a component of '/file/'
anywhere in the name. Even less suitable is the pattern
'%file%' because it will match instruments
with 'file' anywhere in the name, such as
wait/synch/mutex/sql/LOCK_des_key_file.
To check which instrument or consumer names a pattern matches, perform a simple test:
SELECT NAME FROM performance_schema.setup_instruments WHERE NAME LIKE 'pattern'; SELECT NAME FROM performance_schema.setup_consumers WHERE NAME LIKE 'pattern';
For information about the types of names that are supported, see Section 22.6, “Performance Schema Instrument Naming Conventions”.
It is always possible to determine what instruments the
Performance Schema includes by checking the
setup_instruments table. For
example, to see what file-related events are instrumented for
the InnoDB storage engine, use this query:
mysql>SELECT * FROM performance_schema.setup_instrumentsWHERE NAME LIKE 'wait/io/file/innodb/%';+--------------------------------------+---------+-------+ | NAME | ENABLED | TIMED | +--------------------------------------+---------+-------+ | wait/io/file/innodb/innodb_data_file | YES | YES | | wait/io/file/innodb/innodb_log_file | YES | YES | | wait/io/file/innodb/innodb_temp_file | YES | YES | +--------------------------------------+---------+-------+
An exhaustive description of precisely what is instrumented is not given in this documentation, for several reasons:
What is instrumented is the server code. Changes to this code occur often, which also affects the set of instruments.
It is not practical to list all the instruments because there are hundreds of them.
As described earlier, it is possible to find out by querying
the setup_instruments table.
This information is always up to date for your version of
MySQL, also includes instrumentation for instrumented
plugins you might have installed that are not part of the
core server, and can be used by automated tools.
Pre-filtering limits which event information is collected and is
independent of any particular user. By contrast, post-filtering is
performed by individual users through the use of queries with
appropriate WHERE clauses that restrict what
event information to select from the events available after
pre-filtering has been applied.
In Section 22.4.3, “Event Pre-Filtering”, an example
showed how to pre-filter for file instruments. If the event tables
contain both file and nonfile information, post-filtering is
another way to see information only for file events. Add a
WHERE clause to queries to restrict event
selection appropriately:
mysql>SELECT THREAD_ID, NUMBER_OF_BYTESFROM performance_schema.events_waits_historyWHERE EVENT_NAME LIKE 'wait/io/file/%'AND NUMBER_OF_BYTES IS NOT NULL;+-----------+-----------------+ | THREAD_ID | NUMBER_OF_BYTES | +-----------+-----------------+ | 11 | 66 | | 11 | 47 | | 11 | 139 | | 5 | 24 | | 5 | 834 | +-----------+-----------------+
An instrument name consists of a sequence of components separated
by '/' characters. Example names:
wait/io/file/myisam/log wait/io/file/mysys/charset wait/lock/table/sql/handler wait/synch/cond/mysys/COND_alarm wait/synch/cond/sql/BINLOG::update_cond wait/synch/mutex/mysys/BITMAP_mutex wait/synch/mutex/sql/LOCK_delete wait/synch/rwlock/sql/Query_cache_query::lock stage/sql/closing tables stage/sql/Sorting result statement/com/Execute statement/com/Query statement/sql/create_table statement/sql/lock_tables
The instrument name space has a tree-like structure. The components of an instrument name from left to right provide a progression from more general to more specific. The number of components a name has depends on the type of instrument.
The interpretation of a given component in a name depends on the
components to the left of it. For example,
myisam appears in both of the following names,
but myisam in the first name is related to file
I/O, whereas in the second it is related to a synchronization
instrument:
wait/io/file/myisam/log wait/synch/cond/myisam/MI_SORT_INFO::cond
Instrument names consist of a prefix with a structure defined by
the Performance Schema implementation and a suffix defined by the
developer implementing the instrument code. The top-level
component of an instrument prefix indicates the type of
instrument. This component also determines which event timer in
the setup_timers table applies to the
instrument. For the prefix part of instrument names, the top level
indicates the type of instrument.
The suffix part of instrument names comes from the code for the instruments themselves. Suffixes may include levels such as these:
A name for the major component (a server module such as
myisam, innodb,
mysys, or sql) or a
plugin name.
The name of a variable in the code, in the form
XXX (a global variable) or
CCC::MMMMMM in class
CCC). Examples:
COND_thread_cache,
THR_LOCK_myisam,
BINLOG::LOCK_index.
idle: An instrumented idle event. This
instrument has no further components.
stage: An instrumented stage event.
statement: An instrumented statement
event.
wait: An instrumented wait event.
The idle instrument is used for idle events,
which The Performance Schema generates as discussed in the
description of the socket_instances.STATE
column in Section 22.12.3.5, “The socket_instances Table”.
Stage instruments have names of the form
stage/,
where code_area/stage_namecode_area is a value such as
sql or myisam, and
stage_name indicates the stage of
statement processing, such as Sorting result
or Sending data. Stages correspond to the
thread states displayed by SHOW
PROCESSLIST or that are visible in the
INFORMATION_SCHEMA.PROCESSLIST
table.
statement/abstract/*: An abstract
instrument for statement operations. Abstract instruments
are used during the early stages of statement classification
before the exact statement type is known, then changed to a
more specific statement instrument when the type is known.
For a description of this process, see
Section 22.12.6, “Performance Schema Statement Event Tables”.
statement/com: An instrumented command
operation. These have names corresponding to
COM_
operations (see the xxxmysql_com.h header
file and sql/sql_parse.cc. For example,
the statement/com/Connect and
statement/com/Init DB instruments
correspond to the COM_CONNECT and
COM_INIT_DB commands.
statement/sql: An instrumented SQL
statement operation. For example, the
statement/sql/create_db and
statement/sql/select instruments are used
for CREATE DATABASE and
SELECT statements.
wait/io
An instrumented I/O operation.
wait/io/file
An instrumented file I/O operation. For files, the wait
is the time waiting for the file operation to complete
(for example, a call to fwrite()).
Due to caching, the physical file I/O on the disk might
not happen within this call.
wait/io/socket
An instrumented socket operation. Socket instruments
have names of the form
wait/io/socket/sql/.
The server has a listening socket for each network
protocol that it supports. The instruments associated
with listening sockets for TCP/IP or Unix socket file
connections have a
socket_typesocket_type value of
server_tcpip_socket or
server_unix_socket, respectively.
When a listening socket detects a connection, the server
transfers the connection to a new socket managed by a
separate thread. The instrument for the new connection
thread has a socket_type
value of client_connection.
wait/io/table
An instrumented table I/O operation. These include row-level accesses to persistent base tables or temporary tables. Operations that affect rows are fetch, insert, update, and delete. For a view, waits are associated with base tables referenced by the view.
Unlike most waits, a table I/O wait can include other
waits. For example, table I/O might include file I/O or
memory operations. Thus,
events_waits_current for a
table I/O wait usually has two rows. For more
information, see
Section 22.8, “Performance Schema Atom and Molecule Events”.
Some row operations might cause multiple table I/O waits. For example, an insert might activate a trigger that causes an update.
wait/lock
An instrumented lock operation.
wait/lock/table
An instrumented table lock operation.
wait/synch
An instrumented synchronization object. For synchronization
objects, the TIMER_WAIT time includes the
amount of time blocked while attempting to acquire a lock on
the object, if any.
wait/synch/cond
A condition is used by one thread to signal to other threads that something they were waiting for has happened. If a single thread was waiting for a condition, it can wake up and proceed with its execution. If several threads were waiting, they can all wake up and compete for the resource for which they were waiting.
wait/synch/mutex
A mutual exclusion object used to permit access to a resource (such as a section of executable code) while preventing other threads from accessing the resource.
wait/synch/rwlock
A read/write lock object used to lock a specific variable for access while preventing its use by other threads. A shared read lock can be acquired simultaneously by multiple threads. An exclusive write lock can be acquired by only one thread at a time.
There are several status variables associated with the Performance Schema:
mysql> SHOW STATUS LIKE 'perf%';
+-----------------------------------------------+-------+
| Variable_name | Value |
+-----------------------------------------------+-------+
| Performance_schema_accounts_lost | 0 |
| Performance_schema_cond_classes_lost | 0 |
| Performance_schema_cond_instances_lost | 0 |
| Performance_schema_digest_lost | 0 |
| Performance_schema_file_classes_lost | 0 |
| Performance_schema_file_handles_lost | 0 |
| Performance_schema_file_instances_lost | 0 |
| Performance_schema_hosts_lost | 0 |
| Performance_schema_locker_lost | 0 |
| Performance_schema_mutex_classes_lost | 0 |
| Performance_schema_mutex_instances_lost | 0 |
| Performance_schema_rwlock_classes_lost | 0 |
| Performance_schema_rwlock_instances_lost | 0 |
| Performance_schema_session_connect_attrs_lost | 0 |
| Performance_schema_socket_classes_lost | 0 |
| Performance_schema_socket_instances_lost | 0 |
| Performance_schema_stage_classes_lost | 0 |
| Performance_schema_statement_classes_lost | 0 |
| Performance_schema_table_handles_lost | 0 |
| Performance_schema_table_instances_lost | 0 |
| Performance_schema_thread_classes_lost | 0 |
| Performance_schema_thread_instances_lost | 0 |
| Performance_schema_users_lost | 0 |
+-----------------------------------------------+-------+
The Performance Schema status variables provide information about instrumentation that could not be loaded or created due to memory constraints. Names for these variables have several forms:
Performance_schema_
indicates how many instruments of type
xxx_classes_lostxxx could not be loaded.
Performance_schema_
indicates how many instances of object type
xxx_instances_lostxxx could not be created.
Performance_schema_
indicates how many instances of object type
xxx_handles_lostxxx could not be opened.
Performance_schema_locker_lost indicates
how many events are “lost” or not recorded.
For example, if a mutex is instrumented in the server source but
the server cannot allocate memory for the instrumentation at
runtime, it increments
Performance_schema_mutex_classes_lost.
The mutex still functions as a synchronization object (that is,
the server continues to function normally), but performance data
for it will not be collected. If the instrument can be allocated,
it can be used for initializing instrumented mutex instances. For
a singleton mutex such as a global mutex, there will be only one
instance. Other mutexes have an instance per connection, or per
page in various caches and data buffers, so the number of
instances varies over time. Increasing the maximum number of
connections or the maximum size of some buffers will increase the
maximum number of instances that might be allocated at once. If
the server cannot create a given instrumented mutex instance, it
increments
Performance_schema_mutex_instances_lost.
Suppose that the following conditions hold:
The server was started with the
--performance_schema_max_mutex_classes=200
option and thus has room for 200 mutex instruments.
150 mutex instruments have been loaded already.
The plugin named plugin_a contains 40 mutex
instruments.
The plugin named plugin_b contains 20 mutex
instruments.
The server allocates mutex instruments for the plugins depending on how many they need and how many are available, as illustrated by the following sequence of statements:
INSTALL PLUGIN plugin_a
The server now has 150+40 = 190 mutex instruments.
UNINSTALL PLUGIN plugin_a;
The server still has 190 instruments. All the historical data generated by the plugin code is still available, but new events for the instruments are not collected.
INSTALL PLUGIN plugin_a;
The server detects that the 40 instruments are already defined, so no new instruments are created, and previously assigned internal memory buffers are reused. The server still has 190 instruments.
INSTALL PLUGIN plugin_b;
The server has room for 200-190 = 10 instruments (in this case,
mutex classes), and sees that the plugin contains 20 new
instruments. 10 instruments are loaded, and 10 are discarded or
“lost.” The
Performance_schema_mutex_classes_lost
indicates the number of instruments (mutex classes) lost:
mysql> SHOW STATUS LIKE "perf%mutex_classes_lost";
+---------------------------------------+-------+
| Variable_name | Value |
+---------------------------------------+-------+
| Performance_schema_mutex_classes_lost | 10 |
+---------------------------------------+-------+
1 row in set (0.10 sec)
The instrumentation still works and collects (partial) data for
plugin_b.
When the server cannot create a mutex instrument, these results occur:
No row for the instrument is inserted into the
setup_instruments table.
Performance_schema_mutex_classes_lost
increases by 1.
Performance_schema_mutex_instances_lost
does not change. (When the mutex instrument is not created, it
cannot be used to create instrumented mutex instances later.)
The pattern just described applies to all types of instruments, not just mutexes.
A value of
Performance_schema_mutex_classes_lost
greater than 0 can happen in two cases:
To save a few bytes of memory, you start the server with
--performance_schema_max_mutex_classes=,
where NN is less than the default
value. The default value is chosen to be sufficient to load
all the plugins provided in the MySQL distribution, but this
can be reduced if some plugins are never loaded. For example,
you might choose not to load some of the storage engines in
the distribution.
You load a third-party plugin that is instrumented for the
Performance Schema but do not allow for the plugin's
instrumentation memory requirements when you start the server.
Because it comes from a third party, the instrument memory
consumption of this engine is not accounted for in the default
value chosen for
performance_schema_max_mutex_classes.
If the server has insufficient resources for the plugin's
instruments and you do not explicitly allocate more using
--performance_schema_max_mutex_classes=,
loading the plugin leads to starvation of instruments.
N
If the value chosen for
performance_schema_max_mutex_classes
is too small, no error is reported in the error log and there is
no failure at runtime. However, the content of the tables in the
performance_schema database will miss events.
The
Performance_schema_mutex_classes_lost
status variable is the only visible sign to indicate that some
events were dropped internally due to failure to create
instruments.
If an instrument is not lost, it is known to the Performance
Schema, and is used when instrumenting instances. For example,
wait/synch/mutex/sql/LOCK_delete is the name of
a mutex instrument in the
setup_instruments table. This single
instrument is used when creating a mutex in the code (in
THD::LOCK_delete) however many instances of the
mutex are needed as the server runs. In this case,
LOCK_delete is a mutex that is per connection
(THD), so if a server has 1000 connections,
there are 1000 threads, and 1000 instrumented
LOCK_delete mutex instances
(THD::LOCK_delete).
If the server does not have room for all these 1000 instrumented
mutexes (instances), some mutexes are created with
instrumentation, and some are created without instrumentation. If
the server can create only 800 instances, 200 instances are lost.
The server continues to run, but increments
Performance_schema_mutex_instances_lost
by 200 to indicate that instances could not be created.
A value of
Performance_schema_mutex_instances_lost
greater than 0 can happen when the code initializes more mutexes
at runtime than were allocated for
--performance_schema_max_mutex_instances=.
N
The bottom line is that if
SHOW STATUS LIKE
'perf%' says that nothing was lost (all values are
zero), the Performance Schema data is accurate and can be relied
upon. If something was lost, the data is incomplete, and the
Performance Schema could not record everything given the
insufficient amount of memory it was given to use. In this case,
the specific
Performance_schema_
variable indicates the problem area.
xxx_lost
It might be appropriate in some cases to cause deliberate instrument starvation. For example, if you do not care about performance data for file I/O, you can start the server with all Performance Schema parameters related to file I/O set to 0. No memory will be allocated for file-related classes, instances, or handles, and all file events will be lost.
Use SHOW ENGINE
PERFORMANCE_SCHEMA STATUS to inspect the internal
operation of the Performance Schema code:
mysql> SHOW ENGINE PERFORMANCE_SCHEMA STATUS\G
...
*************************** 3. row ***************************
Type: performance_schema
Name: events_waits_history.row_size
Status: 76
*************************** 4. row ***************************
Type: performance_schema
Name: events_waits_history.row_count
Status: 10000
*************************** 5. row ***************************
Type: performance_schema
Name: events_waits_history.memory
Status: 760000
...
*************************** 57. row ***************************
Type: performance_schema
Name: performance_schema.memory
Status: 26459600
...
This statement is intended to help the DBA understand the effects that different Performance Schema options have on memory requirements. For a description of the field meanings, see Section 13.7.5.16, “SHOW ENGINE Statement”.
For a table I/O event, there are usually two rows in
events_waits_current, not one. For
example, a row fetch might result in rows like this:
Row# EVENT_NAME TIMER_START TIMER_END ---- ---------- ----------- --------- 1 wait/io/file/myisam/dfile 10001 10002 2 wait/io/table/sql/handler 10000 NULL
The row fetch causes a file read. In the example, the table I/O
fetch event started before the file I/O event but has not finished
(its TIMER_END value is
NULL). The file I/O event is
“nested” within the table I/O event.
This occurs because, unlike other “atomic” wait
events such as for mutexes or file I/O, table I/O events are
“molecular” and include (overlap with) other events.
In events_waits_current, the table
I/O event usually has two rows:
One row for the most recent table I/O wait event
One row for the most recent wait event of any kind
Usually, but not always, the “of any kind” wait event
differs from the table I/O event. As each subsidiary event
completes, it disappears from
events_waits_current. At this point,
and until the next subsidiary event begins, the table I/O wait is
also the most recent wait of any kind.
For wait, stage, and statement events, the Performance Schema can
monitor and store current events. In addition, when events end,
the Performance Schema can store them in history tables. For each
event type, the Performance Schema uses three tables for storing
current and historical events. The tables have names of the
following forms, where xxx indicates
the event type (waits,
stages, statements):
events_:
The “current events” table stores the current
monitored event for each thread (one row per thread).
xxx_current
events_:
The “recent history” table stores the most recent
events that have ended per thread (up to a maximum number of
rows per thread).
xxx_history
events_:
The “long history” table stores the most recent
events that have ended globally (across all threads, up to a
maximum number of rows per table).
xxx_history_long
The _current table for each event type contains
one row per thread, so there is no system variable for configuring
its maximum size. The Performance Schema autosizes the history
tables, or the sizes can be configured explicitly at server
startup using table-specific system variables, as indicated in the
sections that describe the individual history tables. Typical
autosized values are 10 rows per thread for
_history tables, and 10,000 rows total for
_history_long tables.
For each event type, the _current,
_history, and _history_long
tables have the same columns.
The _current tables show what is currently
happening within the server. When a current event ends, it is
removed from its _current table.
The _history and
_history_long tables show what has happened in
the recent past. When the history tables become full, old events
are discarded as new events are added. Rows expire from the
_history and _history_long
tables in different ways because the tables serve different
purposes:
_history is meant to investigate individual
threads, independently of the global server load.
_history_long is meant to investigate the
server globally, not each thread.
The difference between the two types of history tables relates to the data retention policy. Both tables contains the same data when an event is first seen. However, data within each table expires differently over time, so that data might be preserved for a longer or shorter time in each table:
For _history, when the table contains the
maximum number of rows for a given thread, the oldest thread
row is discarded when a new row for that thread is added.
For _history_long, when the table becomes
full, the oldest row is discarded when a new row is added,
regardless of which thread generated either row.
When a thread ends, all its rows are discarded from the
_history table but not from the
_history_long table.
The following example illustrates the differences in how events are added to and discarded from the two types of history tables. The principles apply equally to all event types. The example is based on these assumptions:
The Performance Schema is configured to retain 10 rows per
thread in the _history table and 10,000
rows total in the _history_long table.
Thread A generates 1 event per second.
Thread B generates 100 events per second.
No other threads are running.
After 5 seconds of execution:
A and B have generated 5 and 500 events, respectively.
_history contains 5 rows for A and 10 rows
for B. Because storage per thread is limited to 10 rows, no
rows have been discarded for A, whereas 490 rows have been
discarded for B.
_history_long contains 5 rows for A and 500
rows for B. Because the table has a maximum size of 10,000
rows, no rows have been discarded for either thread.
After 5 minutes (300 seconds) of execution:
A and B have generated 300 and 30,000 events, respectively.
_history contains 10 rows for A and 10 rows
for B. Because storage per thread is limited to 10 rows, 290
rows have been discarded for A, whereas 29,990 rows have been
discarded for B. Rows for A include data up to 10 seconds old,
whereas rows for B include data up to only .1 seconds old.
_history_long contains 10,000 rows. Because
A and B together generate 101 events per second, the table
contains data up to approximately 10,000/101 = 99 seconds old,
with a mix of rows approximately 100 to 1 from B as opposed to
A.
The MySQL server is capable of maintaining statement digest information. The digesting process converts each SQL statement to normalized form (the statement digest) and computes an MD5 hash value (the digest hash value) from the normalized result. Normalization permits statements that are similar to be grouped and summarized to expose information about the types of statements the server is executing and how often they occur. This section describes how statement digesting occurs and how it can be useful.
As of 5.6.24, digesting occurs in the parser regardless of whether the Performance Schema is available, so that other server components such as MySQL Enterprise Firewall have access to statement digests. Before MySQL 5.6.24, statement digesting was a function of the Performance Schema.
When the parser receives an SQL statement, it computes a statement digest if that digest is needed, which is true if any of the following conditions are true:
Performance Schema digest instrumentation is enabled
MySQL Enterprise Firewall is enabled
The max_digest_length system
variable value determines the maximum number of bytes available
per session for computation of normalized statement digests.
Once that amount of space is used during digest computation,
truncation occurs: no further tokens from a parsed statement are
collected or figure into its digest value. Statements that
differ only after that many bytes of parsed tokens produce the
same normalized statement digest and are considered identical if
compared or if aggregated for digest statistics.
After the normalized statement has been computed, an MD5 hash value is computed from it. In addition:
If MySQL Enterprise Firewall is enabled, it is called and the digest as computed is available to it.
If the Performance Schema has digest instrumentation
enabled, it makes a copy of the normalized statement digest,
allocating a maximum of
performance_schema_max_digest_length
bytes for it. Consequently, if
performance_schema_max_digest_length
is less than
max_digest_length, the copy
is truncated relative to the original. The copy of the
normalized statement digest is stored in the appropriate
Performance Schema tables, along with the MD5 hash value
computed from the original normalized statement. (If the
Performance Schema truncates its copy of the normalized
statement digest relative to the original, it does not
recompute the MD5 hash value.)
In MySQL 5.6.24 and 5.6.25,
performance_schema_max_digest_length
is not available and
max_digest_length applies to
all digest computation. Before MySQL 5.6.24, neither
max_digest_length nor
performance_schema_max_digest_length
are available and a fixed maximum of 1024 bytes applies to all
digest computation.
Statement normalization transforms the statement text to a more standardized digest string representation that preserves the general statement structure while removing information not essential to the structure:
Object identifiers such as database and table names are preserved.
Literal values are converted to parameter markers. A normalized statement does not retain information such as names, passwords, dates, and so forth.
Comments are removed and whitespace is adjusted.
Consider these statements:
SELECT * FROM orders WHERE customer_id=10 AND quantity>20 SELECT * FROM orders WHERE customer_id = 20 AND quantity > 100
To normalize these statements, the parser replaces data values
by ? and adjusts whitespace. Both statements
yield the same normalized form and thus are considered
“the same”:
SELECT * FROM orders WHERE customer_id = ? AND quantity > ?
The normalized statement contains less information but is still representative of the original statement. Other similar statements that have different data values have the same normalized form.
Now consider these statements:
SELECT * FROM customers WHERE customer_id = 1000 SELECT * FROM orders WHERE customer_id = 1000
In this case, the normalized statements differ because the object identifiers differ:
SELECT * FROM customers WHERE customer_id = ? SELECT * FROM orders WHERE customer_id = ?
If normalization produces a statement that exceeds the space
available in the digest buffer (as determined by
max_digest_length), truncation
occurs and the text ends with “...”. Long
normalized statements that differ only in the part that occurs
following the “...” are considered the same.
Consider these statements:
SELECT * FROM mytable WHERE cola = 10 AND colb = 20 SELECT * FROM mytable WHERE cola = 10 AND colc = 20
If the cutoff happens to be right after the
AND, both statements have this normalized
form:
SELECT * FROM mytable WHERE cola = ? AND ...
In this case, the difference in the second column name is lost and both statements are considered the same.
In the Performance Schema, statement digesting involves these components:
A statements_digest consumer in the
setup_consumers table controls
whether the Performance Schema maintains digest information.
See
Statement Digest Consumer.
The statement event tables
(events_statements_current,
events_statements_history, and
events_statements_history_long)
have columns for storing normalized statement digests and
the corresponding digest MD5 hash values:
DIGEST_TEXT is the text of the
normalized statement digest. This is a copy of the
original normalized statement that was computed to a
maximum of
max_digest_length
bytes, further truncated as necessary to
performance_schema_max_digest_length
bytes.
DIGEST is the digest MD5 hash value
computed from the original normalized statement.
See Section 22.12.6, “Performance Schema Statement Event Tables”.
The
events_statements_summary_by_digest
summary table provides aggregated statement digest
information. This table aggregates information for
statements per SCHEMA_NAME and
DIGEST combination. The Performance
Schema uses MD5 hash values for aggregation because they are
fast to compute and have a favorable statistical
distribution that minimizes collisions. See
Section 22.12.9.3, “Statement Summary Tables”.
The statement event tables also have an
SQL_TEXT column that contains the original
SQL statement. The maximum space available for statement display
is 1024 bytes.
The
performance_schema_max_digest_length
system variable determines the maximum number of bytes available
per statement for digest value storage in the Performance
Schema. However, the display length of statement digests may be
longer than the available buffer size due to internal encoding
of statement components such as keywords and literal values.
Consequently, values selected from the
DIGEST_TEXT column of statement event tables
may appear to exceed the
performance_schema_max_digest_length
value.
The
events_statements_summary_by_digest
summary table provides a profile of the statements executed by
the server. It shows what kinds of statements an application is
executing and how often. An application developer can use this
information together with other information in the table to
assess the application's performance characteristics. For
example, table columns that show wait times, lock times, or
index use may highlight types of queries that are inefficient.
This gives the developer insight into which parts of the
application need attention.
The
events_statements_summary_by_digest
summary table has a fixed size. By default the Performance
Schema estimates the size to use at startup. To specify the
table size explicitly, set the
performance_schema_digests_size
system variable at server startup. If the table becomes full,
the Performance Schema groups statements that have
SCHEMA_NAME and DIGEST
values not matching existing values in the table in a special
row with SCHEMA_NAME and
DIGEST set to NULL. This
permits all statements to be counted. However, if the special
row accounts for a significant percentage of the statements
executed, it might be desirable to increase the summary table
size by increasing
performance_schema_digests_size.
For applications that generate very long statements that differ
only at the end, increasing
max_digest_length enables
computation of digests that distinguish statements that would
otherwise aggregate to the same digest. Conversely, decreasing
max_digest_length causes the
server to devote less memory to digest storage but increases the
likelihood of longer statements aggregating to the same digest.
Administrators should keep in mind that larger values result in
correspondingly increased memory requirements, particularly for
workloads that involve large numbers of simultaneous sessions
(the server allocates
max_digest_length bytes per
session).
As described previously, normalized statement digests as
computed by the parser are constrained to a maximum of
max_digest_length bytes,
whereas normalized statement digests stored in the Performance
Schema use
performance_schema_max_digest_length
bytes. The following memory-use considerations apply regarding
the relative values of
max_digest_length and
performance_schema_max_digest_length:
If max_digest_length is
less than
performance_schema_max_digest_length:
Server components other than the Performance Schema use
normalized statement digests that take up to
max_digest_length
bytes.
The Performance Schema does not further truncate
normalized statement digests that it stores, but
allocates more memory than
max_digest_length bytes
per digest, which is unnecessary.
If max_digest_length equals
performance_schema_max_digest_length:
Server components other than the Performance Schema use
normalized statement digests that take up to
max_digest_length
bytes.
The Performance Schema does not further truncate
normalized statement digests that it stores, and
allocates the same amount of memory as
max_digest_length bytes
per digest.
If max_digest_length is
greater than
performance_schema_max_digest_length:
Server components other than the Performance Schema use
normalized statement digests that take up to
max_digest_length
bytes.
The Performance Schema further truncates normalized
statement digests that it stores, and allocates less
memory than
max_digest_length bytes
per digest.
Because the Performance Schema statement event tables might
store many digests, setting
performance_schema_max_digest_length
smaller than max_digest_length
enables administrators to balance these factors:
The need to have long normalized statement digests available for server components outside the Performance Schema
Many concurrent sessions, each of which allocates digest-computation memory
The need to limit memory consumption by the Performance Schema statement event tables when storing many statement digests
The
performance_schema_max_digest_length
setting is not per session, it is per statement, and a session
can store multiple statements in the
events_statements_history table. A
typical number of statements in this table is 10 per session, so
each session will consume 10 times the memory indicated by the
performance_schema_max_digest_length
value, for this table alone.
Also, there are many statements (and digests) collected
globally, most notably in the
events_statements_history_long
table. Here, too, N statements stored
will consume N times the memory
indicated by the
performance_schema_max_digest_length
value.
The name of the performance_schema database is
lowercase, as are the names of tables within it. Queries should
specify the names in lowercase.
Many tables in the performance_schema database
are read only and cannot be modified:
mysql> TRUNCATE TABLE performance_schema.setup_instruments;
ERROR 1683 (HY000): Invalid performance_schema usage.
Some of the setup tables have columns that can be modified to
affect Performance Schema operation; some also permit rows to be
inserted or deleted. Truncation is permitted to clear collected
events, so TRUNCATE TABLE can be
used on tables containing those kinds of information, such as
tables named with a prefix of events_waits_.
Summary tables can be truncated with TRUNCATE
TABLE. Generally, the effect is to reset the summary
columns to 0 or NULL, not to remove rows. This
enables you to clear collected values and restart aggregation.
That might be useful, for example, after you have made a runtime
configuration change. Exceptions to this truncation behavior are
noted in individual summary table sections.
Privileges are as for other databases and tables:
Because only a limited set of privileges apply to Performance
Schema tables, attempts to use GRANT ALL as
shorthand for granting privileges at the database or table leval
fail with an error:
mysql>GRANT ALL ON performance_schema.*TO 'u1'@'localhost';ERROR 1044 (42000): Access denied for user 'root'@'localhost' to database 'performance_schema' mysql>GRANT ALL ON performance_schema.setup_instrumentsTO 'u2'@'localhost';ERROR 1044 (42000): Access denied for user 'root'@'localhost' to database 'performance_schema'
Instead, grant exactly the desired privileges:
mysql>GRANT SELECT ON performance_schema.*TO 'u1'@'localhost';Query OK, 0 rows affected (0.03 sec) mysql>GRANT SELECT, UPDATE ON performance_schema.setup_instrumentsTO 'u2'@'localhost';Query OK, 0 rows affected (0.02 sec)
Tables in the performance_schema database can
be grouped as follows:
Setup tables. These tables are used to configure and display monitoring characteristics.
Current events tables. The
events_waits_current table
contains the most recent event for each thread. Other similar
tables contain current events at different levels of the event
hierarchy: events_stages_current
for stage events, and
events_statements_current for
statement events.
History tables. These tables have the same structure as the
current events tables, but contain more rows. For example, for
wait events, events_waits_history
table contains the most recent 10 events per thread.
events_waits_history_long
contains the most recent 10,000 events. Other similar tables
exist for stage and statement histories.
To change the sizes of the history tables, set the appropriate
system variables at server startup. For example, to set the
sizes of the wait event history tables, set
performance_schema_events_waits_history_size
and
performance_schema_events_waits_history_long_size.
Summary tables. These tables contain information aggregated over groups of events, including those that have been discarded from the history tables.
Instance tables. These tables document what types of objects are instrumented. An instrumented object, when used by the server, produces an event. These tables provide event names and explanatory notes or status information.
Miscellaneous tables. These do not fall into any of the other table groups.
The following table lists each Performance Schema table and provides a short description of each one.
Table 22.1 Performance Schema Tables
| Table Name | Description |
|---|---|
accounts |
Connection statistics per client account |
cond_instances |
synchronization object instances |
events_stages_current |
Current stage events |
events_stages_history |
Most recent stage events per thread |
events_stages_history_long |
Most recent stage events overall |
events_stages_summary_by_account_by_event_name |
Stage events per account and event name |
events_stages_summary_by_host_by_event_name |
Stage events per host name and event name |
events_stages_summary_by_thread_by_event_name |
Stage waits per thread and event name |
events_stages_summary_by_user_by_event_name |
Stage events per user name and event name |
events_stages_summary_global_by_event_name |
Stage waits per event name |
events_statements_current |
Current statement events |
events_statements_history |
Most recent statement events per thread |
events_statements_history_long |
Most recent statement events overall |
events_statements_summary_by_account_by_event_name |
Statement events per account and event name |
events_statements_summary_by_digest |
Statement events per schema and digest value |
events_statements_summary_by_host_by_event_name |
Statement events per host name and event name |
events_statements_summary_by_thread_by_event_name |
Statement events per thread and event name |
events_statements_summary_by_user_by_event_name |
Statement events per user name and event name |
events_statements_summary_global_by_event_name |
Statement events per event name |
events_waits_current |
Current wait events |
events_waits_history |
Most recent wait events per thread |
events_waits_history_long |
Most recent wait events overall |
events_waits_summary_by_account_by_event_name |
Wait events per account and event name |
events_waits_summary_by_host_by_event_name |
Wait events per host name and event name |
events_waits_summary_by_instance |
Wait events per instance |
events_waits_summary_by_thread_by_event_name |
Wait events per thread and event name |
events_waits_summary_by_user_by_event_name |
Wait events per user name and event name |
events_waits_summary_global_by_event_name |
Wait events per event name |
file_instances |
File instances |
file_summary_by_event_name |
File events per event name |
file_summary_by_instance |
File events per file instance |
host_cache |
Information from the internal host cache |
hosts |
Connection statistics per client host name |
mutex_instances |
Mutex synchronization object instances |
objects_summary_global_by_type |
Object summaries |
performance_timers |
Which event timers are available |
rwlock_instances |
Lock synchronization object instances |
session_account_connect_attrs |
Connection attributes per for the current session |
session_connect_attrs |
Connection attributes for all sessions |
setup_actors |
How to initialize monitoring for new foreground threads |
setup_consumers |
Consumers for which event information can be stored |
setup_instruments |
Classes of instrumented objects for which events can be collected |
setup_objects |
Which objects should be monitored |
setup_timers |
Current event timer |
socket_instances |
Active connection instances |
socket_summary_by_event_name |
Socket waits and I/O per event name |
socket_summary_by_instance |
Socket waits and I/O per instance |
table_io_waits_summary_by_index_usage |
Table I/O waits per index |
table_io_waits_summary_by_table |
Table I/O waits per table |
table_lock_waits_summary_by_table |
Table lock waits per table |
threads |
Information about server threads |
users |
Connection statistics per client user name |
The setup tables provide information about the current
instrumentation and enable the monitoring configuration to be
changed. For this reason, some columns in these tables can be
changed if you have the UPDATE
privilege.
The use of tables rather than individual variables for setup information provides a high degree of flexibility in modifying Performance Schema configuration. For example, you can use a single statement with standard SQL syntax to make multiple simultaneous configuration changes.
These setup tables are available:
setup_actors: How to initialize
monitoring for new foreground threads
setup_consumers: The
destinations to which event information can be sent and
stored
setup_instruments: The classes
of instrumented objects for which events can be collected
setup_objects: Which objects
should be monitored
setup_timers: The current event
timer
The setup_actors table contains
information that determines whether to enable monitoring for
new foreground server threads (threads associated with client
connections). This table has a maximum size of 100 rows by
default. To change the table size, modify the
performance_schema_setup_actors_size
system variable at server startup.
For each new foreground thread, the Performance Schema matches
the user and host for the thread against the rows of the
setup_actors table. If a row from
that table matches, its ENABLED column
value is used to set the INSTRUMENTED
column of the threads table row
for the thread. This enables instrumenting to be applied
selectively per host, user, or account (user and host
combination). If there is no match, the
INSTRUMENTED column for the thread is set
to NO.
For background threads, there is no associated user.
INSTRUMENTED is YES by
default and setup_actors is not
consulted.
The initial contents of the
setup_actors table match any user
and host combination, so monitoring is enabled by default for
all foreground threads:
mysql> SELECT * FROM performance_schema.setup_actors;
+------+------+------+
| HOST | USER | ROLE |
+------+------+------+
| % | % | % |
+------+------+------+
For information about how to use the
setup_actors table to affect
event monitoring, see
Section 22.4.6, “Pre-Filtering by Thread”.
Modifications to the setup_actors
table affect only foreground threads created subsequent to the
modification, not existing threads. To affect existing
threads, modify the INSTRUMENTED column of
threads table rows.
The setup_actors table has these
columns:
HOST
The host name. This should be a literal name, or
'%' to mean “any host.”
USER
The user name. This should be a literal name, or
'%' to mean “any user.”
ROLE
Unused.
TRUNCATE TABLE is permitted for
the setup_actors table. It
removes the rows.
The setup_consumers table lists
the types of consumers for which event information can be
stored and which are enabled:
mysql> SELECT * FROM performance_schema.setup_consumers;
+--------------------------------+---------+
| NAME | ENABLED |
+--------------------------------+---------+
| events_stages_current | NO |
| events_stages_history | NO |
| events_stages_history_long | NO |
| events_statements_current | YES |
| events_statements_history | NO |
| events_statements_history_long | NO |
| events_waits_current | NO |
| events_waits_history | NO |
| events_waits_history_long | NO |
| global_instrumentation | YES |
| thread_instrumentation | YES |
| statements_digest | YES |
+--------------------------------+---------+
The consumer settings in the
setup_consumers table form a
hierarchy from higher levels to lower. For detailed
information about the effect of enabling different consumers,
see Section 22.4.7, “Pre-Filtering by Consumer”.
Modifications to the
setup_consumers table affect
monitoring immediately.
The setup_consumers table has
these columns:
NAME
The consumer name.
ENABLED
Whether the consumer is enabled. The value is
YES or NO. This
column can be modified. If you disable a consumer, the
server does not spend time adding event information to it.
TRUNCATE TABLE is not permitted
for the setup_consumers table.
The setup_instruments table lists
classes of instrumented objects for which events can be
collected:
mysql> SELECT * FROM performance_schema.setup_instruments;
+---------------------------------------------------+---------+-------+
| NAME | ENABLED | TIMED |
+---------------------------------------------------+---------+-------+
...
| stage/sql/end | NO | NO |
| stage/sql/executing | NO | NO |
| stage/sql/init | NO | NO |
| stage/sql/insert | NO | NO |
...
| statement/sql/load | YES | YES |
| statement/sql/grant | YES | YES |
| statement/sql/check | YES | YES |
| statement/sql/flush | YES | YES |
...
| wait/synch/mutex/sql/LOCK_global_read_lock | YES | YES |
| wait/synch/mutex/sql/LOCK_global_system_variables | YES | YES |
| wait/synch/mutex/sql/LOCK_lock_db | YES | YES |
| wait/synch/mutex/sql/LOCK_manager | YES | YES |
...
| wait/synch/rwlock/sql/LOCK_grant | YES | YES |
| wait/synch/rwlock/sql/LOGGER::LOCK_logger | YES | YES |
| wait/synch/rwlock/sql/LOCK_sys_init_connect | YES | YES |
| wait/synch/rwlock/sql/LOCK_sys_init_slave | YES | YES |
...
| wait/io/file/sql/binlog | YES | YES |
| wait/io/file/sql/binlog_index | YES | YES |
| wait/io/file/sql/casetest | YES | YES |
| wait/io/file/sql/dbopt | YES | YES |
...
Each instrument added to the source code provides a row for
the setup_instruments table, even
when the instrumented code is not executed. When an instrument
is enabled and executed, instrumented instances are created,
which are visible in the
xxx_instancesfile_instances or
rwlock_instances.
Modifications to most
setup_instruments rows affect
monitoring immediately. For some instruments, modifications
are effective only at server startup; changing them at runtime
has no effect. This affects primarily mutexes, conditions, and
rwlocks in the server, although there may be other instruments
for which this is true.
For more information about the role of the
setup_instruments table in event
filtering, see
Section 22.4.3, “Event Pre-Filtering”.
The setup_instruments table has
these columns:
NAME
The instrument name. Instrument names may have multiple
parts and form a hierarchy, as discussed in
Section 22.6, “Performance Schema Instrument Naming Conventions”.
Events produced from execution of an instrument have an
EVENT_NAME value that is taken from the
instrument NAME value. (Events do not
really have a “name,” but this provides a way
to associate events with instruments.)
ENABLED
Whether the instrument is enabled. The value is
YES or NO. A
disabled instrument produces no events. This column can be
modified, although setting ENABLED has
no effect for instruments that have already been created.
TIMED
Whether the instrument is timed. The value is
YES or NO. This
column can be modified, although setting
TIMED has no effect for instruments
that have already been created.
If an enabled instrument is not timed, the instrument code
is enabled, but the timer is not. Events produced by the
instrument have NULL for the
TIMER_START,
TIMER_END, and
TIMER_WAIT timer values. This in turn
causes those values to be ignored when calculating the
sum, minimum, maximum, and average time values in summary
tables.
TRUNCATE TABLE is not permitted
for the setup_instruments table.
The setup_objects table controls
whether the Performance Schema monitors particular objects.
This table has a maximum size of 100 rows by default. To
change the table size, modify the
performance_schema_setup_objects_size
system variable at server startup.
The initial setup_objects
contents look like this:
mysql> SELECT * FROM performance_schema.setup_objects;
+-------------+--------------------+-------------+---------+-------+
| OBJECT_TYPE | OBJECT_SCHEMA | OBJECT_NAME | ENABLED | TIMED |
+-------------+--------------------+-------------+---------+-------+
| TABLE | mysql | % | NO | NO |
| TABLE | performance_schema | % | NO | NO |
| TABLE | information_schema | % | NO | NO |
| TABLE | % | % | YES | YES |
+-------------+--------------------+-------------+---------+-------+
Modifications to the
setup_objects table affect object
monitoring immediately.
For object types listed in
setup_objects, the Performance
Schema uses the table to how to monitor them. Object matching
is based on the OBJECT_SCHEMA and
OBJECT_NAME columns. Objects for which
there is no match are not monitored.
The effect of the default object configuration is to
instrument all tables except those in the
mysql,
INFORMATION_SCHEMA, and
performance_schema databases. (Tables in
the INFORMATION_SCHEMA database are not
instrumented regardless of the contents of
setup_objects; the row for
information_schema.% simply makes this
default explicit.)
When the Performance Schema checks for a match in
setup_objects, it tries to find
more specific matches first. For example, with a table
db1.t1, it looks for a match for
'db1' and 't1', then for
'db1' and '%', then for
'%' and '%'. The order
in which matching occurs matters because different matching
setup_objects rows can have
different ENABLED and
TIMED values.
Rows can be inserted into or deleted from
setup_objects by users with the
INSERT or
DELETE privilege on the table.
For existing rows, only the ENABLED and
TIMED columns can be modified, by users
with the UPDATE privilege on
the table.
For more information about the role of the
setup_objects table in event
filtering, see
Section 22.4.3, “Event Pre-Filtering”.
The setup_objects table has these
columns:
OBJECT_TYPE
The type of object to instrument. This is always
'TABLE' (base table).
TABLE filtering affects table I/O
events (wait/io/table/sql/handler
instrument) and table lock events
(wait/lock/table/sql/handler
instrument).
OBJECT_SCHEMA
The schema that contains the object. This should be a
literal name, or '%' to mean “any
schema.”
OBJECT_NAME
The name of the instrumented object. This should be a
literal name, or '%' to mean “any
object.”
ENABLED
Whether events for the object are instrumented. The value
is YES or NO. This
column can be modified.
TIMED
Whether events for the object are timed. The value is
YES or NO. This
column can be modified.
TRUNCATE TABLE is permitted for
the setup_objects table. It
removes the rows.
The setup_timers table shows the
currently selected event timers:
mysql> SELECT * FROM performance_schema.setup_timers;
+-----------+-------------+
| NAME | TIMER_NAME |
+-----------+-------------+
| idle | MICROSECOND |
| wait | CYCLE |
| stage | NANOSECOND |
| statement | NANOSECOND |
+-----------+-------------+
The setup_timers.TIMER_NAME value can be
changed to select a different timer. The value can be any of
the values in the
performance_timers.TIMER_NAME column. For
an explanation of how event timing occurs, see
Section 22.4.1, “Performance Schema Event Timing”.
Modifications to the setup_timers
table affect monitoring immediately. Events already in
progress may use the original timer for the begin time and the
new timer for the end time. To avoid unpredictable results
after you make timer changes, use
TRUNCATE TABLE to reset
Performance Schema statistics.
The setup_timers table has these
columns:
NAME
The type of instrument the timer is used for.
TIMER_NAME
The timer that applies to the instrument type. This column can be modified.
TRUNCATE TABLE is not permitted
for the setup_timers table.
Instance tables document what types of objects are instrumented. They provide event names and explanatory notes or status information:
cond_instances: Condition
synchronization object instances
file_instances: File instances
mutex_instances: Mutex
synchronization object instances
rwlock_instances: Lock
synchronization object instances
socket_instances: Active
connection instances
These tables list instrumented synchronization objects, files,
and connections. There are three types of synchronization
objects: cond, mutex, and
rwlock. Each instance table has an
EVENT_NAME or NAME column
to indicate the instrument associated with each row. Instrument
names may have multiple parts and form a hierarchy, as discussed
in Section 22.6, “Performance Schema Instrument Naming Conventions”.
The mutex_instances.LOCKED_BY_THREAD_ID and
rwlock_instances.WRITE_LOCKED_BY_THREAD_ID
columns are extremely important for investigating performance
bottlenecks or deadlocks. For examples of how to use them for
this purpose, see Section 22.18, “Using the Performance Schema to Diagnose Problems”
The cond_instances table lists
all the conditions seen by the Performance Schema while the
server executes. A condition is a synchronization mechanism
used in the code to signal that a specific event has happened,
so that a thread waiting for this condition can resume work.
When a thread is waiting for something to happen, the condition name is an indication of what the thread is waiting for, but there is no immediate way to tell which other thread, or threads, will cause the condition to happen.
The cond_instances table has
these columns:
NAME
The instrument name associated with the condition.
OBJECT_INSTANCE_BEGIN
The address in memory of the instrumented condition.
TRUNCATE TABLE is not permitted
for the cond_instances table.
The file_instances table lists
all the files seen by the Performance Schema when executing
file I/O instrumentation. If a file on disk has never been
opened, it will not be in
file_instances. When a file is
deleted from the disk, it is also removed from the
file_instances table.
The file_instances table has
these columns:
FILE_NAME
The file name.
EVENT_NAME
The instrument name associated with the file.
OPEN_COUNT
The count of open handles on the file. If a file was
opened and then closed, it was opened 1 time, but
OPEN_COUNT will be 0. To list all the
files currently opened by the server, use WHERE
OPEN_COUNT > 0.
TRUNCATE TABLE is not permitted
for the file_instances table.
The mutex_instances table lists
all the mutexes seen by the Performance Schema while the
server executes. A mutex is a synchronization mechanism used
in the code to enforce that only one thread at a given time
can have access to some common resource. The resource is said
to be “protected” by the mutex.
When two threads executing in the server (for example, two user sessions executing a query simultaneously) do need to access the same resource (a file, a buffer, or some piece of data), these two threads will compete against each other, so that the first query to obtain a lock on the mutex will cause the other query to wait until the first is done and unlocks the mutex.
The work performed while holding a mutex is said to be in a “critical section,” and multiple queries do execute this critical section in a serialized way (one at a time), which is a potential bottleneck.
The mutex_instances table has
these columns:
NAME
The instrument name associated with the mutex.
OBJECT_INSTANCE_BEGIN
The address in memory of the instrumented mutex.
LOCKED_BY_THREAD_ID
When a thread currently has a mutex locked,
LOCKED_BY_THREAD_ID is the
THREAD_ID of the locking thread,
otherwise it is NULL.
TRUNCATE TABLE is not permitted
for the mutex_instances table.
For every mutex instrumented in the code, the Performance Schema provides the following information.
The setup_instruments table
lists the name of the instrumentation point, with the
prefix wait/synch/mutex/.
When some code creates a mutex, a row is added to the
mutex_instances table. The
OBJECT_INSTANCE_BEGIN column is a
property that uniquely identifies the mutex.
When a thread attempts to lock a mutex, the
events_waits_current table
shows a row for that thread, indicating that it is waiting
on a mutex (in the EVENT_NAME column),
and indicating which mutex is waited on (in the
OBJECT_INSTANCE_BEGIN column).
When a thread succeeds in locking a mutex:
events_waits_current
shows that the wait on the mutex is completed (in the
TIMER_END and
TIMER_WAIT columns)
The completed wait event is added to the
events_waits_history and
events_waits_history_long
tables
mutex_instances shows
that the mutex is now owned by the thread (in the
THREAD_ID column).
When a thread unlocks a mutex,
mutex_instances shows that
the mutex now has no owner (the
THREAD_ID column is
NULL).
When a mutex object is destroyed, the corresponding row is
removed from mutex_instances.
By performing queries on both of the following tables, a monitoring application or a DBA can detect bottlenecks or deadlocks between threads that involve mutexes:
events_waits_current, to see
what mutex a thread is waiting for
mutex_instances, to see which
other thread currently owns a mutex
The rwlock_instances table lists
all the rwlock instances (read write locks)
seen by the Performance Schema while the server executes. An
rwlock is a synchronization mechanism used
in the code to enforce that threads at a given time can have
access to some common resource following certain rules. The
resource is said to be “protected” by the
rwlock. The access is either shared (many
threads can have a read lock at the same time) or exclusive
(only one thread can have a write lock at a given time).
Depending on how many threads are requesting a lock, and the nature of the locks requested, access can be either granted in shared mode, granted in exclusive mode, or not granted at all, waiting for other threads to finish first.
The rwlock_instances table has
these columns:
NAME
The instrument name associated with the lock.
OBJECT_INSTANCE_BEGIN
The address in memory of the instrumented lock.
WRITE_LOCKED_BY_THREAD_ID
When a thread currently has an rwlock
locked in exclusive (write) mode,
WRITE_LOCKED_BY_THREAD_ID is the
THREAD_ID of the locking thread,
otherwise it is NULL.
READ_LOCKED_BY_COUNT
When a thread currently has an rwlock
locked in shared (read) mode,
READ_LOCKED_BY_COUNT is incremented by
1. This is a counter only, so it cannot be used directly
to find which thread holds a read lock, but it can be used
to see whether there is a read contention on an
rwlock, and see how many readers are
currently active.
TRUNCATE TABLE is not permitted
for the rwlock_instances table.
By performing queries on both of the following tables, a monitoring application or a DBA may detect some bottlenecks or deadlocks between threads that involve locks:
events_waits_current, to see
what rwlock a thread is waiting for
rwlock_instances, to see
which other thread currently owns an
rwlock
There is a limitation: The
rwlock_instances can be used only
to identify the thread holding a write lock, but not the
threads holding a read lock.
The socket_instances table
provides a real-time snapshot of the active connections to the
MySQL server. The table contains one row per TCP/IP or Unix
socket file connection. Information available in this table
provides a real-time snapshot of the active connections to the
server. (Additional information is available in socket summary
tables, including network activity such as socket operations
and number of bytes transmitted and received; see
Section 22.12.9.7, “Socket Summary Tables”).
mysql> SELECT * FROM performance_schema.socket_instances\G
*************************** 1. row ***************************
EVENT_NAME: wait/io/socket/sql/server_unix_socket
OBJECT_INSTANCE_BEGIN: 4316619408
THREAD_ID: 1
SOCKET_ID: 16
IP:
PORT: 0
STATE: ACTIVE
*************************** 2. row ***************************
EVENT_NAME: wait/io/socket/sql/client_connection
OBJECT_INSTANCE_BEGIN: 4316644608
THREAD_ID: 21
SOCKET_ID: 39
IP: 127.0.0.1
PORT: 55233
STATE: ACTIVE
*************************** 3. row ***************************
EVENT_NAME: wait/io/socket/sql/server_tcpip_socket
OBJECT_INSTANCE_BEGIN: 4316699040
THREAD_ID: 1
SOCKET_ID: 14
IP: 0.0.0.0
PORT: 50603
STATE: ACTIVE
Socket instruments have names of the form
wait/io/socket/sql/
and are used like this:
socket_type
The server has a listening socket for each network
protocol that it supports. The instruments associated with
listening sockets for TCP/IP or Unix socket file
connections have a socket_type
value of server_tcpip_socket or
server_unix_socket, respectively.
When a listening socket detects a connection, the server
transfers the connection to a new socket managed by a
separate thread. The instrument for the new connection
thread has a socket_type value
of client_connection.
When a connection terminates, the row in
socket_instances
corresponding to it is deleted.
The socket_instances table has
these columns:
EVENT_NAME
The name of the wait/io/socket/*
instrument that produced the event. This is a
NAME value from the
setup_instruments table.
Instrument names may have multiple parts and form a
hierarchy, as discussed in
Section 22.6, “Performance Schema Instrument Naming Conventions”.
OBJECT_INSTANCE_BEGIN
This column uniquely identifies the socket. The value is the address of an object in memory.
THREAD_ID
The internal thread identifier assigned by the server. Each socket is managed by a single thread, so each socket can be mapped to a thread which can be mapped to a server process.
SOCKET_ID
The internal file handle assigned to the socket.
IP
The client IP address. The value may be either an IPv4 or IPv6 address, or blank to indicate a Unix socket file connection.
PORT
The TCP/IP port number, in the range from 0 to 65535.
STATE
The socket status, either IDLE or
ACTIVE. Wait times for active sockets
are tracked using the corresponding socket instrument.
Wait times for idle sockets are tracked using the
idle instrument.
A socket is idle if it is waiting for a request from the
client. When a socket becomes idle, the event row in
socket_instances that is
tracking the socket switches from a status of
ACTIVE to IDLE. The
EVENT_NAME value remains
wait/io/socket/*, but timing for the
instrument is suspended. Instead, an event is generated in
the events_waits_current
table with an EVENT_NAME value of
idle.
When the next request is received, the
idle event terminates, the socket
instance switches from IDLE to
ACTIVE, and timing of the socket
instrument resumes.
TRUNCATE TABLE is not permitted
for the socket_instances table.
The IP:PORT column combination value
identifies the connection. This combination value is used in
the OBJECT_NAME column of the
events_waits_
tables, to identify the connection from which socket events
come:
xxx
For the Unix domain listener socket
(server_unix_socket), the port is 0,
and the IP is ''.
For client connections via the Unix domain listener
(client_connection), the port is 0, and
the IP is ''.
For the TCP/IP server listener socket
(server_tcpip_socket), the port is
always the master port (for example, 3306), and the IP is
always 0.0.0.0.
For client connections via the TCP/IP listener
(client_connection), the port is
whatever the server assigns, but never 0. The IP is the IP
of the originating host (127.0.0.1 or
::1 for the local host)
The Performance Schema instruments waits, which are events that take time. Within the event hierarchy, wait events nest within stage events, which nest within statement events.
These tables store wait events:
events_waits_current: The
current wait event for each thread.
events_waits_history: The most
recent wait events that have ended per thread.
events_waits_history_long: The
most recent wait events that have ended globally (across all
threads).
The following sections describe the wait event tables. There are also summary tables that aggregate information about wait events; see Section 22.12.9.1, “Wait Event Summary Tables”.
For more information about the relationship between the three wait event tables, see Section 22.9, “Performance Schema Tables for Current and Historical Events”.
To control whether to collect wait events, set the state of the relevant instruments and consumers:
The setup_instruments table
contains instruments with names that begin with
wait. Use these instruments to enable or
disable collection of individual wait event classes.
The setup_consumers table
contains consumer values with names corresponding to the
current and historical wait event table names. Use these
consumers to filter collection of wait events.
Some wait instruments are enabled by default; others are disabled. For example:
mysql>SELECT * FROM performance_schema.setup_instrumentsWHERE NAME LIKE 'wait/io/file/innodb%';+--------------------------------------+---------+-------+ | NAME | ENABLED | TIMED | +--------------------------------------+---------+-------+ | wait/io/file/innodb/innodb_data_file | YES | YES | | wait/io/file/innodb/innodb_log_file | YES | YES | | wait/io/file/innodb/innodb_temp_file | YES | YES | +--------------------------------------+---------+-------+ mysql>SELECT * FROM performance_schema.setup_instrumentsWHERE NAME LIKE 'wait/io/socket/%';+----------------------------------------+---------+-------+ | NAME | ENABLED | TIMED | +----------------------------------------+---------+-------+ | wait/io/socket/sql/server_tcpip_socket | NO | NO | | wait/io/socket/sql/server_unix_socket | NO | NO | | wait/io/socket/sql/client_connection | NO | NO | +----------------------------------------+---------+-------+
The wait consumers are disabled by default:
mysql>SELECT *FROM performance_schema.setup_consumersWHERE NAME LIKE 'events_waits%';+---------------------------+---------+ | NAME | ENABLED | +---------------------------+---------+ | events_waits_current | NO | | events_waits_history | NO | | events_waits_history_long | NO | +---------------------------+---------+
To control wait event collection at server startup, use lines
like these in your my.cnf file:
Enable:
[mysqld] performance-schema-instrument='wait/%=ON' performance-schema-consumer-events-waits-current=ON performance-schema-consumer-events-waits-history=ON performance-schema-consumer-events-waits-history-long=ON
Disable:
[mysqld] performance-schema-instrument='wait/%=OFF' performance-schema-consumer-events-waits-current=OFF performance-schema-consumer-events-waits-history=OFF performance-schema-consumer-events-waits-history-long=OFF
To control wait event collection at runtime, update the
setup_instruments and
setup_consumers tables:
Enable:
UPDATE performance_schema.setup_instruments SET ENABLED = 'YES', TIMED = 'YES' WHERE NAME = 'wait/%'; UPDATE performance_schema.setup_consumers SET ENABLED = 'YES' WHERE NAME LIKE 'events_waits%';
Disable:
UPDATE performance_schema.setup_instruments SET ENABLED = 'NO', TIMED = 'NO' WHERE NAME = 'wait/%'; UPDATE performance_schema.setup_consumers SET ENABLED = 'NO' WHERE NAME LIKE 'events_waits%';
To collect only specific wait events, enable only the corresponding wait instruments. To collect wait events only for specific wait event tables, enable the wait instruments but only the wait consumers corresponding to the desired tables.
The setup_timers table contains a
row with a NAME value of
wait that indicates the unit for wait event
timing. The default unit is CYCLE:
mysql>SELECT *FROM performance_schema.setup_timersWHERE NAME = 'wait';+------+------------+ | NAME | TIMER_NAME | +------+------------+ | wait | CYCLE | +------+------------+
To change the timing unit, modify the
TIMER_NAME value:
UPDATE performance_schema.setup_timers SET TIMER_NAME = 'NANOSECOND' WHERE NAME = 'wait';
For additional information about configuring event collection, see Section 22.3, “Performance Schema Startup Configuration”, and Section 22.4, “Performance Schema Runtime Configuration”.
The events_waits_current table
contains current wait events. The table stores one row per
thread showing the current status of the thread's most recent
monitored wait event, so there is no system variable for
configuring the table size.
Of the tables that contain wait event rows,
events_waits_current is the most
fundamental. Other tables that contain wait event rows are
logically derived from the current events. For example, the
events_waits_history and
events_waits_history_long tables
are collections of the most recent wait events that have
ended, up to a maximum number of rows per thread and globally
across all threads, respectively.
For more information about the relationship between the three wait event tables, see Section 22.9, “Performance Schema Tables for Current and Historical Events”.
For information about configuring whether to collect wait events, see Section 22.12.4, “Performance Schema Wait Event Tables”.
The events_waits_current table
has these columns:
THREAD_ID, EVENT_ID
The thread associated with the event and the thread
current event number when the event starts. The
THREAD_ID and
EVENT_ID values taken together uniquely
identify the row. No two rows have the same pair of
values.
END_EVENT_ID
This column is set to NULL when the
event starts and updated to the thread current event
number when the event ends.
EVENT_NAME
The name of the instrument that produced the event. This
is a NAME value from the
setup_instruments table.
Instrument names may have multiple parts and form a
hierarchy, as discussed in
Section 22.6, “Performance Schema Instrument Naming Conventions”.
SOURCE
The name of the source file containing the instrumented code that produced the event and the line number in the file at which the instrumentation occurs. This enables you to check the source to determine exactly what code is involved. For example, if a mutex or lock is being blocked, you can check the context in which this occurs.
TIMER_START,
TIMER_END,
TIMER_WAIT
Timing information for the event. The unit for these
values is picoseconds (trillionths of a second). The
TIMER_START and
TIMER_END values indicate when event
timing started and ended. TIMER_WAIT is
the event elapsed time (duration).
If an event has not finished, TIMER_END
and TIMER_WAIT are
NULL before MySQL 5.6.26. As of 5.6.26,
TIMER_END is the current timer value
and TIMER_WAIT is the time elapsed so
far (TIMER_END −
TIMER_START).
If an event is produced from an instrument that has
TIMED = NO, timing information is not
collected, and TIMER_START,
TIMER_END, and
TIMER_WAIT are all
NULL.
For discussion of picoseconds as the unit for event times and factors that affect time values, see Section 22.4.1, “Performance Schema Event Timing”.
SPINS
For a mutex, the number of spin rounds. If the value is
NULL, the code does not use spin rounds
or spinning is not instrumented.
OBJECT_SCHEMA,
OBJECT_NAME,
OBJECT_TYPE,
OBJECT_INSTANCE_BEGIN
These columns identify the object “being acted on.” What that means depends on the object type.
For a synchronization object (cond,
mutex, rwlock):
OBJECT_SCHEMA,
OBJECT_NAME, and
OBJECT_TYPE are
NULL.
OBJECT_INSTANCE_BEGIN is the
address of the synchronization object in memory.
For a file I/O object:
OBJECT_SCHEMA is
NULL.
OBJECT_NAME is the file name.
OBJECT_TYPE is
FILE.
OBJECT_INSTANCE_BEGIN is an address
in memory.
For a socket object:
OBJECT_NAME is the
IP:PORT value for the socket.
OBJECT_INSTANCE_BEGIN is an address
in memory.
For a table I/O object:
OBJECT_SCHEMA is the name of the
schema that contains the table.
OBJECT_NAME is the table name.
OBJECT_TYPE is
TABLE for a persistent base table
or TEMPORARY TABLE for a temporary
table.
OBJECT_INSTANCE_BEGIN is an address
in memory.
An OBJECT_INSTANCE_BEGIN value itself
has no meaning, except that different values indicate
different objects.
OBJECT_INSTANCE_BEGIN can be used for
debugging. For example, it can be used with GROUP
BY OBJECT_INSTANCE_BEGIN to see whether the load
on 1,000 mutexes (that protect, say, 1,000 pages or blocks
of data) is spread evenly or just hitting a few
bottlenecks. This can help you correlate with other
sources of information if you see the same object address
in a log file or another debugging or performance tool.
INDEX_NAME
The name of the index used. PRIMARY
indicates the table primary index. NULL
means that no index was used.
NESTING_EVENT_ID
The EVENT_ID value of the event within
which this event is nested.
NESTING_EVENT_TYPE
The nesting event type. The value is
STATEMENT, STAGE, or
WAIT.
OPERATION
The type of operation performed, such as
lock, read, or
write.
NUMBER_OF_BYTES
The number of bytes read or written by the operation. For
table I/O waits (events for the
wait/io/table/sql/handler instrument),
NUMBER_OF_BYTES is
NULL.
FLAGS
Reserved for future use.
TRUNCATE TABLE is permitted for
the events_waits_current table.
It removes the rows.
The events_waits_history table
contains the N most recent wait
events that have ended per thread. Wait events are not added
to the table until they have ended. When the table contains
the maximum number of rows for a given thread, the oldest
thread row is discarded when a new row for that thread is
added. When a thread ends, all its rows are discarded.
The Performance Schema autosizes the value of
N during server startup. To set the
number of rows per thread explicitly, set the
performance_schema_events_waits_history_size
system variable at server startup.
The events_waits_history table
has the same columns as
events_waits_current. See
Section 22.12.4.1, “The events_waits_current Table”.
TRUNCATE TABLE is permitted for
the events_waits_history table.
It removes the rows.
For more information about the relationship between the three wait event tables, see Section 22.9, “Performance Schema Tables for Current and Historical Events”.
For information about configuring whether to collect wait events, see Section 22.12.4, “Performance Schema Wait Event Tables”.
The events_waits_history_long
table contains N the most recent
wait events that have ended globally, across all threads. Wait
events are not added to the table until they have ended. When
the table becomes full, the oldest row is discarded when a new
row is added, regardless of which thread generated either row.
The Performance Schema autosizes the value of
N during server startup. To set the
table size explicitly, set the
performance_schema_events_waits_history_long_size
system variable at server startup.
The events_waits_history_long
table has the same columns as
events_waits_current. See
Section 22.12.4.1, “The events_waits_current Table”.
TRUNCATE TABLE is permitted for
the events_waits_history_long
table. It removes the rows.
For more information about the relationship between the three wait event tables, see Section 22.9, “Performance Schema Tables for Current and Historical Events”.
For information about configuring whether to collect wait events, see Section 22.12.4, “Performance Schema Wait Event Tables”.
The Performance Schema instruments stages, which are steps
during the statement-execution process, such as parsing a
statement, opening a table, or performing a
filesort operation. Stages correspond to the
thread states displayed by SHOW
PROCESSLIST or that are visible in the
INFORMATION_SCHEMA.PROCESSLIST
table. Stages begin and end when state values change.
Within the event hierarchy, wait events nest within stage events, which nest within statement events.
These tables store stage events:
events_stages_current: The
current stage event for each thread.
events_stages_history: The most
recent stage events that have ended per thread.
events_stages_history_long: The
most recent stage events that have ended globally (across
all threads).
The following sections describe the stage event tables. There are also summary tables that aggregate information about stage events; see Section 22.12.9.2, “Stage Summary Tables”.
For more information about the relationship between the three stage event tables, see Section 22.9, “Performance Schema Tables for Current and Historical Events”.
To control whether to collect stage events, set the state of the relevant instruments and consumers:
The setup_instruments table
contains instruments with names that begin with
stage. Use these instruments to enable or
disable collection of individual stage event classes.
The setup_consumers table
contains consumer values with names corresponding to the
current and historical stage event table names. Use these
consumers to filter collection of stage events.
The stage instruments are disabled by default. For example:
mysql>SELECT *FROM performance_schema.setup_instrumentsWHERE NAME RLIKE 'stage/sql/[a-c]';+----------------------------------------------------+---------+-------+ | NAME | ENABLED | TIMED | +----------------------------------------------------+---------+-------+ | stage/sql/After create | NO | NO | | stage/sql/allocating local table | NO | NO | | stage/sql/altering table | NO | NO | | stage/sql/committing alter table to storage engine | NO | NO | | stage/sql/Changing master | NO | NO | | stage/sql/Checking master version | NO | NO | | stage/sql/checking permissions | NO | NO | | stage/sql/checking privileges on cached query | NO | NO | | stage/sql/checking query cache for query | NO | NO | | stage/sql/cleaning up | NO | NO | | stage/sql/closing tables | NO | NO | | stage/sql/Connecting to master | NO | NO | | stage/sql/converting HEAP to MyISAM | NO | NO | | stage/sql/Copying to group table | NO | NO | | stage/sql/Copying to tmp table | NO | NO | | stage/sql/copy to tmp table | NO | NO | | stage/sql/Creating delayed handler | NO | NO | | stage/sql/Creating sort index | NO | NO | | stage/sql/creating table | NO | NO | | stage/sql/Creating tmp table | NO | NO | +----------------------------------------------------+---------+-------+
The stage consumers are disabled by default:
mysql>SELECT *FROM performance_schema.setup_consumersWHERE NAME LIKE 'events_stages%';+----------------------------+---------+ | NAME | ENABLED | +----------------------------+---------+ | events_stages_current | NO | | events_stages_history | NO | | events_stages_history_long | NO | +----------------------------+---------+
To control stage event collection at server startup, use lines
like these in your my.cnf file:
Enable:
[mysqld] performance-schema-instrument='stage/%=ON' performance-schema-consumer-events-stages-current=ON performance-schema-consumer-events-stages-history=ON performance-schema-consumer-events-stages-history-long=ON
Disable:
[mysqld] performance-schema-instrument='stage/%=OFF' performance-schema-consumer-events-stages-current=OFF performance-schema-consumer-events-stages-history=OFF performance-schema-consumer-events-stages-history-long=OFF
To control stage event collection at runtime, update the
setup_instruments and
setup_consumers tables:
Enable:
UPDATE performance_schema.setup_instruments SET ENABLED = 'YES', TIMED = 'YES' WHERE NAME = 'stage/%'; UPDATE performance_schema.setup_consumers SET ENABLED = 'YES' WHERE NAME LIKE 'events_stages%';
Disable:
UPDATE performance_schema.setup_instruments SET ENABLED = 'NO', TIMED = 'NO' WHERE NAME = 'stage/%'; UPDATE performance_schema.setup_consumers SET ENABLED = 'NO' WHERE NAME LIKE 'events_stages%';
To collect only specific stage events, enable only the corresponding stage instruments. To collect stage events only for specific stage event tables, enable the stage instruments but only the stage consumers corresponding to the desired tables.
The setup_timers table contains a
row with a NAME value of
stage that indicates the unit for stage event
timing. The default unit is NANOSECOND:
mysql>SELECT *FROM performance_schema.setup_timersWHERE NAME = 'stage';+-------+------------+ | NAME | TIMER_NAME | +-------+------------+ | stage | NANOSECOND | +-------+------------+
To change the timing unit, modify the
TIMER_NAME value:
UPDATE performance_schema.setup_timers SET TIMER_NAME = 'MICROSECOND' WHERE NAME = 'stage';
For additional information about configuring event collection, see Section 22.3, “Performance Schema Startup Configuration”, and Section 22.4, “Performance Schema Runtime Configuration”.
The events_stages_current table
contains current stage events. The table stores one row per
thread showing the current status of the thread's most recent
monitored stage event, so there is no system variable for
configuring the table size.
Of the tables that contain stage event rows,
events_stages_current is the most
fundamental. Other tables that contain stage event rows are
logically derived from the current events. For example, the
events_stages_history and
events_stages_history_long tables
are collections of the most recent stage events that have
ended, up to a maximum number of rows per thread and globally
across all threads, respectively.
For more information about the relationship between the three stage event tables, see Section 22.9, “Performance Schema Tables for Current and Historical Events”.
For information about configuring whether to collect stage events, see Section 22.12.5, “Performance Schema Stage Event Tables”.
The events_stages_current table
has these columns:
THREAD_ID, EVENT_ID
The thread associated with the event and the thread
current event number when the event starts. The
THREAD_ID and
EVENT_ID values taken together uniquely
identify the row. No two rows have the same pair of
values.
END_EVENT_ID
This column is set to NULL when the
event starts and updated to the thread current event
number when the event ends.
EVENT_NAME
The name of the instrument that produced the event. This
is a NAME value from the
setup_instruments table.
Instrument names may have multiple parts and form a
hierarchy, as discussed in
Section 22.6, “Performance Schema Instrument Naming Conventions”.
SOURCE
The name of the source file containing the instrumented code that produced the event and the line number in the file at which the instrumentation occurs. This enables you to check the source to determine exactly what code is involved.
TIMER_START,
TIMER_END,
TIMER_WAIT
Timing information for the event. The unit for these
values is picoseconds (trillionths of a second). The
TIMER_START and
TIMER_END values indicate when event
timing started and ended. TIMER_WAIT is
the event elapsed time (duration).
If an event has not finished, TIMER_END
and TIMER_WAIT are
NULL before MySQL 5.6.26. As of 5.6.26,
TIMER_END is the current timer value
and TIMER_WAIT is the time elapsed so
far (TIMER_END −
TIMER_START).
If an event is produced from an instrument that has
TIMED = NO, timing information is not
collected, and TIMER_START,
TIMER_END, and
TIMER_WAIT are all
NULL.
For discussion of picoseconds as the unit for event times and factors that affect time values, see Section 22.4.1, “Performance Schema Event Timing”.
NESTING_EVENT_ID
The EVENT_ID value of the event within
which this event is nested. The nesting event for a stage
event is usually a statement event.
NESTING_EVENT_TYPE
The nesting event type. The value is
STATEMENT, STAGE, or
WAIT.
TRUNCATE TABLE is permitted for
the events_stages_current table.
It removes the rows.
The events_stages_history table
contains the N most recent stage
events that have ended per thread. Stage events are not added
to the table until they have ended. When the table contains
the maximum number of rows for a given thread, the oldest
thread row is discarded when a new row for that thread is
added. When a thread ends, all its rows are discarded.
The Performance Schema autosizes the value of
N during server startup. To set the
number of rows per thread explicitly, set the
performance_schema_events_stages_history_size
system variable at server startup.
The events_stages_history table
has the same columns as
events_stages_current. See
Section 22.12.5.1, “The events_stages_current Table”.
TRUNCATE TABLE is permitted for
the events_stages_history table.
It removes the rows.
For more information about the relationship between the three stage event tables, see Section 22.9, “Performance Schema Tables for Current and Historical Events”.
For information about configuring whether to collect stage events, see Section 22.12.5, “Performance Schema Stage Event Tables”.
The events_stages_history_long
table contains the N most recent
stage events that have ended globally, across all threads.
Stage events are not added to the table until they have ended.
When the table becomes full, the oldest row is discarded when
a new row is added, regardless of which thread generated
either row.
The Performance Schema autosizes the value of
N during server startup. To set the
table size explicitly, set the
performance_schema_events_stages_history_long_size
system variable at server startup.
The events_stages_history_long
table has the same columns as
events_stages_current. See
Section 22.12.5.1, “The events_stages_current Table”.
TRUNCATE TABLE is permitted for
the events_stages_history_long
table. It removes the rows.
For more information about the relationship between the three stage event tables, see Section 22.9, “Performance Schema Tables for Current and Historical Events”.
For information about configuring whether to collect stage events, see Section 22.12.5, “Performance Schema Stage Event Tables”.
The Performance Schema instruments statement execution. Statement events occur at a high level of the event hierarchy: Wait events nest within stage events, which nest within statement events.
These tables store statement events:
events_statements_current: The
current statement event for each thread.
events_statements_history: The
most recent statement events that have ended per thread.
events_statements_history_long:
The most recent statement events that have ended globally
(across all threads).
The following sections describe the statement event tables. There are also summary tables that aggregate information about statement events; see Section 22.12.9.3, “Statement Summary Tables”.
For more information about the relationship between the three
events_statements_
event tables, see
Section 22.9, “Performance Schema Tables for Current and Historical Events”.
xxx
To control whether to collect statement events, set the state of the relevant instruments and consumers:
The setup_instruments table
contains instruments with names that begin with
statement. Use these instruments to
enable or disable collection of individual statement event
classes.
The setup_consumers table
contains consumer values with names corresponding to the
current and historical statement event table names, and the
statement digest consumer. Use these consumers to filter
collection of statement events and statement digesting.
The statement instruments are enabled by default, and the
events_statements_current and
statements_digest statement consumers are
enabled by default:
mysql>SELECT *FROM performance_schema.setup_instrumentsWHERE NAME LIKE 'statement/%';+---------------------------------------------+---------+-------+ | NAME | ENABLED | TIMED | +---------------------------------------------+---------+-------+ | statement/sql/select | YES | YES | | statement/sql/create_table | YES | YES | | statement/sql/create_index | YES | YES | ... | statement/sp/stmt | YES | YES | | statement/sp/set | YES | YES | | statement/sp/set_trigger_field | YES | YES | | statement/scheduler/event | YES | YES | | statement/com/Sleep | YES | YES | | statement/com/Quit | YES | YES | | statement/com/Init DB | YES | YES | ... | statement/abstract/Query | YES | YES | | statement/abstract/new_packet | YES | YES | | statement/abstract/relay_log | YES | YES | +---------------------------------------------+---------+-------+
mysql>SELECT *FROM performance_schema.setup_consumersWHERE NAME LIKE '%statements%';+--------------------------------+---------+ | NAME | ENABLED | +--------------------------------+---------+ | events_statements_current | YES | | events_statements_history | NO | | events_statements_history_long | NO | | statements_digest | YES | +--------------------------------+---------+
To control statement event collection at server startup, use
lines like these in your my.cnf file:
Enable:
[mysqld] performance-schema-instrument='statement/%=ON' performance-schema-consumer-events-statements-current=ON performance-schema-consumer-events-statements-history=ON performance-schema-consumer-events-statements-history-long=ON performance-schema-consumer-statements-digest=ON
Disable:
[mysqld] performance-schema-instrument='statement/%=OFF' performance-schema-consumer-events-statements-current=OFF performance-schema-consumer-events-statements-history=OFF performance-schema-consumer-events-statements-history-long=OFF performance-schema-consumer-statements-digest=OFF
To control statement event collection at runtime, update the
setup_instruments and
setup_consumers tables:
Enable:
UPDATE performance_schema.setup_instruments SET ENABLED = 'YES', TIMED = 'YES' WHERE NAME LIKE 'statement/%'; UPDATE performance_schema.setup_consumers SET ENABLED = 'YES' WHERE NAME LIKE '%statements%';
Disable:
UPDATE performance_schema.setup_instruments SET ENABLED = 'NO', TIMED = 'NO' WHERE NAME LIKE 'statement/%'; UPDATE performance_schema.setup_consumers SET ENABLED = 'NO' WHERE NAME LIKE '%statements%';
To collect only specific statement events, enable only the corresponding statement instruments. To collect statement events only for specific statement event tables, enable the statement instruments but only the statement consumers corresponding to the desired tables.
The setup_timers table contains a
row with a NAME value of
statement that indicates the unit for
statement event timing. The default unit is
NANOSECOND:
mysql>SELECT *FROM performance_schema.setup_timersWHERE NAME = 'statement';+-----------+------------+ | NAME | TIMER_NAME | +-----------+------------+ | statement | NANOSECOND | +-----------+------------+
To change the timing unit, modify the
TIMER_NAME value:
UPDATE performance_schema.setup_timers SET TIMER_NAME = 'MICROSECOND' WHERE NAME = 'statement';
For additional information about configuring event collection, see Section 22.3, “Performance Schema Startup Configuration”, and Section 22.4, “Performance Schema Runtime Configuration”.
Statement monitoring begins from the moment the server sees that activity is requested on a thread, to the moment when all activity has ceased. Typically, this means from the time the server gets the first packet from the client to the time the server has finished sending the response. Monitoring occurs only for top-level statements. Statements within stored programs and subqueries are not seen separately.
When the Performance Schema instruments a request (server command or SQL statement), it uses instrument names that proceed in stages from more general (or “abstract”) to more specific until it arrives at a final instrument name.
Final instrument names correspond to server commands and SQL statements:
Server commands correspond to the
COM_
defined in the xxx codesmysql_com.h header file
and processed in sql/sql_parse.cc.
Examples are COM_PING and
COM_QUIT. Instruments for commands have
names that begin with statement/com, such
as statement/com/Ping and
statement/com/Quit.
SQL statements are expressed as text, such as
DELETE FROM t1 or SELECT * FROM
t2. Instruments for SQL statements have names that
begin with statement/sql, such as
statement/sql/delete and
statement/sql/select.
Some final instrument names are specific to error handling:
statement/com/Error accounts for messages
received by the server that are out of band. It can be used
to detect commands sent by clients that the server does not
understand. This may be helpful for purposes such as
identifying clients that are misconfigured or using a
version of MySQL more recent than that of the server, or
clients that are attempting to attack the server.
statement/sql/error accounts for SQL
statements that fail to parse. It can be used to detect
malformed queries sent by clients. A query that fails to
parse differs from a query that parses but fails due to an
error during execution. For example, SELECT *
FROM is malformed, and the
statement/sql/error instrument is used.
By contrast, SELECT * parses but fails
with a No tables used error. In this
case, statement/sql/select is used and
the statement event contains information to indicate the
nature of the error.
A request can be obtained from any of these sources:
As a command or statement request from a client, which sends the request as packets
As a statement string read from the relay log on a replication slave
The details for a request are not initially known and the Performance Schema proceeds from abstract to specific instrument names in a sequence that depends on the source of the request.
For a request received from a client:
When the server detects a new packet at the socket level, a
new statement is started with an abstract instrument name of
statement/abstract/new_packet.
When the server reads the packet number, it knows more about
the type of request received, and the Performance Schema
refines the instrument name. For example, if the request is
a COM_PING packet, the instrument name
becomes statement/com/Ping and that is
the final name. If the request is a
COM_QUERY packet, it is known to
correspond to an SQL statement but not the particular type
of statement. In this case, the instrument changes from one
abstract name to a more specific but still abstract name,
statement/abstract/Query, and the request
requires further classification.
If the request is a statement, the statement text is read
and given to the parser. After parsing, the exact statement
type is known. If the request is, for example, an
INSERT statement, the
Performance Schema refines the instrument name from
statement/abstract/Query to
statement/sql/insert, which is the final
name.
For a request read as a statement from the relay log on a replication slave:
Statements in the relay log are stored as text and are read
as such. There is no network protocol, so the
statement/abstract/new_packet instrument
is not used. Instead, the initial instrument is
statement/abstract/relay_log.
When the statement is parsed, the exact statement type is
known. If the request is, for example, an
INSERT statement, the
Performance Schema refines the instrument name from
statement/abstract/Query to
statement/sql/insert, which is the final
name.
The preceding description applies only for statement-based replication. For row-based replication, table I/O done on the slave as it processes row changes can be instrumented, but row events in the relay log do not appear as discrete statements.
For statistics to be collected for statements, it is not
sufficient to enable only the final
statement/sql/* instruments used for
individual statement types. The abtract
statement/abstract/* instruments must be
enabled as well. This should not normally be an issue because
all statement instruments are enabled by default. However, an
application that enables or disables statement instruments
selectively must take into account that disabling abstract
instruments also disables statistics collection for the
individual statement instruments. For example, to collect
statistics for INSERT statements,
statement/sql/insert must be enabled, but
also statement/abstract/new_packet and
statement/abstract/Query. Similarly, for
replicated statements to be instrumented,
statement/abstract/relay_log must be enabled.
No statistics are aggregated for abstract instruments such as
statement/abstract/Query because no statement
is ever classified with an abstract instrument as the final
statement name.
The abstract instrument names in the preceding discussion are as of MySQL 5.6.15. In earlier 5.6 versions, there was some renaming before those names were settled on:
statement/abstract/new_packet was
statement/com/ in MySQL 5.6.14,
statement/com/new_packet in MySQL 5.6.13,
and statement/com/ before that.
statement/abstract/Query was
statement/com/Query before MySQL 5.6.15.
statement/abstract/relay_log was
statement/rpl/relay_log from MySQL 5.6.13
to 5.6.14 and did not exist before that.
The events_statements_current
table contains current statement events. The table stores one
row per thread showing the current status of the thread's most
recent monitored statement event, so there is no system
variable for configuring the table size.
Of the tables that contain statement event rows,
events_statements_current is the
most fundamental. Other tables that contain statement event
rows are logically derived from the current events. For
example, the
events_statements_history and
events_statements_history_long
tables are collections of the most recent statement events
that have ended, up to a maximum number of rows per thread and
globally across all threads, respectively.
For more information about the relationship between the three
events_statements_
event tables, see
Section 22.9, “Performance Schema Tables for Current and Historical Events”.
xxx
For information about configuring whether to collect statement events, see Section 22.12.6, “Performance Schema Statement Event Tables”.
The events_statements_current
table has these columns:
THREAD_ID, EVENT_ID
The thread associated with the event and the thread
current event number when the event starts. The
THREAD_ID and
EVENT_ID values taken together uniquely
identify the row. No two rows have the same pair of
values.
END_EVENT_ID
This column is set to NULL when the
event starts and updated to the thread current event
number when the event ends.
EVENT_NAME
The name of the instrument from which the event was
collected. This is a NAME value from
the setup_instruments table.
Instrument names may have multiple parts and form a
hierarchy, as discussed in
Section 22.6, “Performance Schema Instrument Naming Conventions”.
For SQL statements, the EVENT_NAME
value initially is statement/com/Query
until the statement is parsed, then changes to a more
appropriate value, as described in
Section 22.12.6, “Performance Schema Statement Event Tables”.
SOURCE
The name of the source file containing the instrumented code that produced the event and the line number in the file at which the instrumentation occurs. This enables you to check the source to determine exactly what code is involved.
TIMER_START,
TIMER_END,
TIMER_WAIT
Timing information for the event. The unit for these
values is picoseconds (trillionths of a second). The
TIMER_START and
TIMER_END values indicate when event
timing started and ended. TIMER_WAIT is
the event elapsed time (duration).
If an event has not finished, TIMER_END
and TIMER_WAIT are
NULL before MySQL 5.6.26. As of 5.6.26,
TIMER_END is the current timer value
and TIMER_WAIT is the time elapsed so
far (TIMER_END −
TIMER_START).
If an event is produced from an instrument that has
TIMED = NO, timing information is not
collected, and TIMER_START,
TIMER_END, and
TIMER_WAIT are all
NULL.
For discussion of picoseconds as the unit for event times and factors that affect time values, see Section 22.4.1, “Performance Schema Event Timing”.
LOCK_TIME
The time spent waiting for table locks. This value is computed in microseconds but normalized to picoseconds for easier comparison with other Performance Schema timers.
SQL_TEXT
The text of the SQL statement. For a command not
associated with an SQL statement, the value is
NULL. The maximum space available for
statement display is 1024 bytes.
DIGEST
The statement digest MD5 value as a string of 32
hexadecimal characters, or NULL if the
statements_digest consumer is
no. For more information about
statement digesting, see
Section 22.10, “Performance Schema Statement Digests”.
DIGEST_TEXT
The normalized statement digest text, or
NULL if the
statements_digest consumer is
no. For more information about
statement digesting, see
Section 22.10, “Performance Schema Statement Digests”.
The
performance_schema_max_digest_length
system variable determines the maximum number of bytes
available per session for digest value storage. However,
the display length of statement digests may be longer than
the available buffer size due to encoding of statement
components such as keywords and literal values in digest
buffer. Consequently, values selected from the
DIGEST_TEXT column of statement event
tables may appear to exceed the
performance_schema_max_digest_length
value.
performance_schema_max_digest_length
was added in MySQL 5.6.26. In MySQL 5.6.24 and 5.6.25,
performance_schema_max_digest_length
is not available and the
max_digest_length value
determines the maximum number of bytes available for
digest value storage. Before MySQL 5.6.24, neither
max_digest_length nor
performance_schema_max_digest_length
are available and a fixed maximum of 1024 bytes is
available for digest value storage.
CURRENT_SCHEMA
The default database for the statement,
NULL if there is none.
OBJECT_SCHEMA,
OBJECT_NAME,
OBJECT_TYPE
Reserved. Always NULL.
OBJECT_INSTANCE_BEGIN
This column identifies the statement. The value is the address of an object in memory.
MYSQL_ERRNO
The statement error number, from the statement diagnostics area.
RETURNED_SQLSTATE
The statement SQLSTATE value, from the statement diagnostics area.
MESSAGE_TEXT
The statement error message, from the statement diagnostics area.
ERRORS
Whether an error occurred for the statement. The value is
0 if the SQLSTATE value begins with 00
(completion) or 01 (warning). The value
is 1 is the SQLSTATE value is anything else.
WARNINGS
The number of warnings, from the statement diagnostics area.
ROWS_AFFECTED
The number of rows affected by the statement. For a description of the meaning of “affected,” see Section 23.7.6.1, “mysql_affected_rows()”.
ROWS_SENT
The number of rows returned by the statement.
ROWS_EXAMINED
The number of rows examined by the server layer (not counting any processing internal to storage engines).
CREATED_TMP_DISK_TABLES
Like the
Created_tmp_disk_tables
status variable, but specific to the statement.
CREATED_TMP_TABLES
Like the
Created_tmp_tables
status variable, but specific to the statement.
SELECT_FULL_JOIN
Like the
Select_full_join status
variable, but specific to the statement.
SELECT_FULL_RANGE_JOIN
Like the
Select_full_range_join
status variable, but specific to the statement.
SELECT_RANGE
Like the Select_range
status variable, but specific to the statement.
SELECT_RANGE_CHECK
Like the
Select_range_check
status variable, but specific to the statement.
SELECT_SCAN
Like the Select_scan
status variable, but specific to the statement.
SORT_MERGE_PASSES
Like the
Sort_merge_passes status
variable, but specific to the statement.
SORT_RANGE
Like the Sort_range
status variable, but specific to the statement.
SORT_ROWS
Like the Sort_rows
status variable, but specific to the statement.
SORT_SCAN
Like the Sort_scan
status variable, but specific to the statement.
NO_INDEX_USED
1 if the statement performed a table scan without using an index, 0 otherwise.
NO_GOOD_INDEX_USED
1 if the server found no good index to use for the
statement, 0 otherwise. For additional information, see
the description of the Extra column
from EXPLAIN output for the
Range checked for each record value in
Section 8.8.2, “EXPLAIN Output Format”.
NESTING_EVENT_ID,
NESTING_EVENT_TYPE
Reserved. Always NULL.
TRUNCATE TABLE is permitted for
the events_statements_current
table. It removes the rows.
The events_statements_history
table contains the N most recent
statement events that have ended per thread. Statement events
are not added to the table until they have ended. When the
table contains the maximum number of rows for a given thread,
the oldest thread row is discarded when a new row for that
thread is added. When a thread ends, all its rows are
discarded.
The Performance Schema autosizes the value of
N during server startup. To set the
number of rows per thread explicitly, set the
performance_schema_events_statements_history_size
system variable at server startup.
The events_statements_history
table has the same columns as
events_statements_current. See
Section 22.12.6.1, “The events_statements_current Table”.
TRUNCATE TABLE is permitted for
the events_statements_history
table. It removes the rows.
For more information about the relationship between the three
events_statements_
event tables, see
Section 22.9, “Performance Schema Tables for Current and Historical Events”.
xxx
For information about configuring whether to collect statement events, see Section 22.12.6, “Performance Schema Statement Event Tables”.
The
events_statements_history_long
table contains the N most recent
statement events that have ended globally, across all threads.
Statement events are not added to the table until they have
ended. When the table becomes full, the oldest row is
discarded when a new row is added, regardless of which thread
generated either row.
The value of N is autosized at
server startup. To set the table size explicitly, set the
performance_schema_events_statements_history_long_size
system variable at server startup.
The
events_statements_history_long
table has the same columns as
events_statements_current. See
Section 22.12.6.1, “The events_statements_current Table”.
TRUNCATE TABLE is permitted for
the
events_statements_history_long
table. It removes the rows.
For more information about the relationship between the three
events_statements_
event tables, see
Section 22.9, “Performance Schema Tables for Current and Historical Events”.
xxx
For information about configuring whether to collect statement events, see Section 22.12.6, “Performance Schema Statement Event Tables”.
When a client connects to the MySQL server, it does so under a particular user name and from a particular host. The Performance Schema provides statistics about these connections, tracking them per account (user and host combination) as well as separately per user name and host name, using these tables:
The meaning of “account” in the connection tables
is similar to its meaning in the MySQL grant tables in the
mysql system database, in the sense that the
term refers to a combination of user and host values. They
differ in that, for grant tables, the host part of an account
can be a pattern, whereas for Performance Schema tables, the
host value is always a specific nonpattern host name.
Each connection table has CURRENT_CONNECTIONS
and TOTAL_CONNECTIONS columns to track the
current and total number of connections per “tracking
value” on which its statistics are based. The tables
differ in what they use for the tracking value. The
accounts table has
USER and HOST columns to
track connections per user and host combination. The
users and
hosts tables have a
USER and HOST column,
respectively, to track connections per user name and host name.
The Performance Schema also counts internal threads and threads
for user sessions that failed to authenticate, using rows with
USER and HOST column
values of NULL.
Suppose that clients named user1 and
user2 each connect one time from
hosta and hostb. The
Performance Schema tracks the connections as follows:
The accounts table has four
rows, for the
user1/hosta,
user1/hostb,
user2/hosta, and
user2/hostb account
values, each row counting one connection per account.
The hosts table has two rows,
for hosta and hostb,
each row counting two connections per host name.
The users table has two rows,
for user1 and user2,
each row counting two connections per user name.
When a client connects, the Performance Schema determines which
row in each connection table applies, using the tracking value
appropriate to each table. If there is no such row, one is
added. Then the Performance Schema increments by one the
CURRENT_CONNECTIONS and
TOTAL_CONNECTIONS columns in that row.
When a client disconnects, the Performance Schema decrements by
one the CURRENT_CONNECTIONS column in the row
and leaves the TOTAL_CONNECTIONS column
unchanged.
TRUNCATE TABLE is permitted for
connection tables. It has these effects:
Rows are removed for accounts, hosts, or users that have no
current connections (rows with CURRENT_CONNECTIONS
= 0).
Nonremoved rows are reset to count only current connections:
For rows with CURRENT_CONNECTIONS > 0,
TOTAL_CONNECTIONS is reset to
CURRENT_CONNECTIONS.
Summary tables that depend on the connection table are implicitly truncated, as described later in this section.
The Performance Schema maintains summary tables that aggregate
connection statistics for various event types by account, host,
or user. These tables have
_summary_by_account,
_summary_by_host, or
_summary_by_user in the name. To identify
them, use this query:
mysql>SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLESWHERE TABLE_SCHEMA = 'performance_schema'AND TABLE_NAME REGEXP '_summary_by_(account|host|user)'ORDER BY TABLE_NAME;+----------------------------------------------------+ | TABLE_NAME | +----------------------------------------------------+ | events_stages_summary_by_account_by_event_name | | events_stages_summary_by_host_by_event_name | | events_stages_summary_by_user_by_event_name | | events_statements_summary_by_account_by_event_name | | events_statements_summary_by_host_by_event_name | | events_statements_summary_by_user_by_event_name | | events_waits_summary_by_account_by_event_name | | events_waits_summary_by_host_by_event_name | | events_waits_summary_by_user_by_event_name | +----------------------------------------------------+
For details about individual connection summary tables, consult the section that describes tables for the summarized event type:
Wait event summaries: Section 22.12.9.1, “Wait Event Summary Tables”
Stage event summaries: Section 22.12.9.2, “Stage Summary Tables”
Statement event summaries: Section 22.12.9.3, “Statement Summary Tables”
TRUNCATE TABLE is permitted for
connection summary tables. It removes rows for accounts, hosts,
or users with no connections, and resets the summary columns to
zero for the remaining rows. In addition, each summary table
that is aggregated by account, host, user, or thread is
implicitly truncated by truncation of the connection table on
which it depends. The following table describes the relationship
between connection table truncation and implicitly truncated
tables.
Table 22.2 Implicit Effects of Connection Table Truncation
| Truncated Connection Table | Implicitly Truncated Summary Tables |
|---|---|
accounts |
Tables with names containing _summary_by_account,
_summary_by_thread |
hosts |
Tables with names containing _summary_by_account,
_summary_by_host,
_summary_by_thread |
users |
Tables with names containing _summary_by_account,
_summary_by_user,
_summary_by_thread |
Truncating a _summary_global summary table
also implicitly truncates its corresponding connection and
thread summary tables. For example, truncating
events_waits_summary_global_by_event_name
implicitly truncates the wait event summary tables that are
aggregated by account, host, user, or thread.
The accounts table contains a row
for each account that has connected to the MySQL server. For
each account, the table counts the current and total number of
connections. The table size is autosized at server startup. To
set the table size explicitly, set the
performance_schema_accounts_size
system variable at server startup. To disable account
statistics, set this variable to 0.
The accounts table has the
following columns. For a description of how the Performance
Schema maintains rows in this table, including the effect of
TRUNCATE TABLE, see
Section 22.12.7, “Performance Schema Connection Tables”.
USER
The client user name for the connection. This is
NULL for an internal thread, or for a
user session that failed to authenticate.
HOST
The host from which the client connected. This is
NULL for an internal thread, or for a
user session that failed to authenticate.
CURRENT_CONNECTIONS
The current number of connections for the account.
TOTAL_CONNECTIONS
The total number of connections for the account.
The hosts table contains a row
for each host from which clients have connected to the MySQL
server. For each host name, the table counts the current and
total number of connections. The table size is autosized at
server startup. To set the table size explicitly, set the
performance_schema_hosts_size
system variable at server startup. To disable host statistics,
set this variable to 0.
The hosts table has the following
columns. For a description of how the Performance Schema
maintains rows in this table, including the effect of
TRUNCATE TABLE, see
Section 22.12.7, “Performance Schema Connection Tables”.
HOST
The host from which the client connected. This is
NULL for an internal thread, or for a
user session that failed to authenticate.
CURRENT_CONNECTIONS
The current number of connections for the host.
TOTAL_CONNECTIONS
The total number of connections for the host.
The users table contains a row
for each user who has connected to the MySQL server. For each
user name, the table counts the current and total number of
connections. The table size is autosized at server startup. To
set the table size explicitly, set the
performance_schema_users_size
system variable at server startup. To disable user statistics,
set this variable to 0.
The users table has the following
columns. For a description of how the Performance Schema
maintains rows in this table, including the effect of
TRUNCATE TABLE, see
Section 22.12.7, “Performance Schema Connection Tables”.
USER
The client user name for the connection. This is
NULL for an internal thread, or for a
user session that failed to authenticate.
CURRENT_CONNECTIONS
The current number of connections for the user.
TOTAL_CONNECTIONS
The total number of connections for the user.
Connection attributes are key-value pairs that application
programs can pass to the server at connect time. For
applications based on the C API implemented by the
libmysqlclient client library, the
mysql_options() and
mysql_options4() functions
define the connection attribute set. Other MySQL Connectors may
provide their own attribute-definition methods.
These Performance Schema tables expose attribute information:
session_account_connect_attrs:
Connection attributes for the current session, and other
sessions associated with the session account
session_connect_attrs:
Connection attributes for all sessions
Attribute names that begin with an underscore
(_) are reserved for internal use and should
not be created by application programs. This convention permits
new attributes to be introduced by MySQL without colliding with
application attributes, and enables application programs to
define their own attributes that do not collide with internal
attributes.
The set of connection attributes visible within a given connection varies depending on factors such as your platform, MySQL Connector used to establish the connection, or client program.
The libmysqlclient client library sets these
attributes:
_client_name: The client name
(libmysql for the client library).
_client_version: The client library
version.
_os: The operating system (for example,
Linux, Win64).
_pid: The client process ID.
_platform: The machine platform (for
example, x86_64).
_thread: The client thread ID (Windows
only).
Other MySQL Connectors may define their own connection attributes.
MySQL Connector/J defines these attributes:
_client_license: The connector license
type.
_runtime_vendor: The Java runtime
environment (JRE) vendor.
_runtime_version: The Java runtime
environment (JRE) version.
MySQL Connector/NET defines these attributes:
_client_version: The client library
version.
_os: The operating system (for example,
Linux, Win64).
_pid: The client process ID.
_platform: The machine platform (for
example, x86_64).
_program_name: The client name.
_thread: The client thread ID (Windows
only).
PHP defines attributes that depend on how it was compiled:
Compiled using libmysqlclient: The
standard libmysqlclient attributes,
described previously.
Compiled using mysqlnd: Only the
_client_name attribute, with a value of
mysqlnd.
Many MySQL client programs set a program_name
attribute with a value equal to the client name. For example,
mysqladmin and mysqldump
set program_name to
mysqladmin and mysqldump,
respectively.
Some MySQL client programs define additional attributes:
_client_role:
binary_log_listener
Replication slave connections:
program_name:
mysqld
_client_role:
binary_log_listener
FEDERATED storage engine
connections:
program_name:
mysqld
_client_role:
federated_storage
There are limits on the amount of connection attribute data transmitted from client to server:
A fixed limit imposed by the client prior to connect time.
A fixed limit imposed by the server at connect time.
A configurable limit imposed by the Performance Schema at connect time.
For connections initiated using the C API, the
libmysqlclient library imposes a limit of
64KB on the aggregate size of connection attribute data on the
client side: Calls to
mysql_options() that cause this
limit to be exceeded produce a
CR_INVALID_PARAMETER_NO error.
Other MySQL Connectors may impose their own client-side limits
on how much connection attribute data can be transmitted to the
server.
On the server side, these size checks on connection attribute data occur:
The server imposes a limit of 64KB on the aggregate size of connection attribute data it will accept. If a client attempts to send more than 64KB of attribute data, the server rejects the connection.
For accepted connections, the Performance Schema checks
aggregate attribute size against the value of the
performance_schema_session_connect_attrs_size
system variable. If attribute size exceeds this value, these
actions take place:
The Performance Schema truncates the attribute data and
increments the
Performance_schema_session_connect_attrs_lost
status variable, which indicates the number of
connections for which attribute truncation occurred.
The Performance Schema writes a message to the error log
if the log_warnings
system variable is greater than zero:
[Warning] Connection attributes of length N were truncated
Application programs can provide key-value connection attributes to be passed to the server at connect time. For descriptions of common attributes, see Section 22.12.8, “Performance Schema Connection Attribute Tables”.
The session_account_connect_attrs
table contains connection attributes only for the current
session, and other sessions associated with the session
account. To see connection attributes for all sessions, use
the session_connect_attrs table.
The session_account_connect_attrs
table contains these columns:
PROCESSLIST_ID
The connection identifier for the session.
ATTR_NAME
The attribute name.
ATTR_VALUE
The attribute value.
ORDINAL_POSITION
The order in which the attribute was added to the set of connection attributes.
TRUNCATE TABLE is not permitted
for the
session_account_connect_attrs
table.
Application programs can provide key-value connection attributes to be passed to the server at connect time. For descriptions of common attributes, see Section 22.12.8, “Performance Schema Connection Attribute Tables”.
The session_connect_attrs table
contains connection attributes for all sessions. To see
connection attributes only for the current session, and other
sessions associated with the session account, use the
session_account_connect_attrs
table.
The session_connect_attrs table
contains these columns:
PROCESSLIST_ID
The connection identifier for the session.
ATTR_NAME
The attribute name.
ATTR_VALUE
The attribute value.
ORDINAL_POSITION
The order in which the attribute was added to the set of connection attributes.
TRUNCATE TABLE is not permitted
for the session_connect_attrs
table.
Summary tables provide aggregated information for terminated events over time. The tables in this group summarize event data in different ways.
events_waits_summary_by_account_by_event_name:
Wait events per account and event name
events_waits_summary_by_host_by_event_name:
Wait events per host name and event name
events_waits_summary_by_instance:
Wait events per instance
events_waits_summary_by_thread_by_event_name:
Wait events per thread and event name
events_waits_summary_by_user_by_event_name:
Wait events per user name and event name
events_waits_summary_global_by_event_name:
Wait events per event name
events_stages_summary_by_account_by_event_name:
Stage events per account and event name
events_stages_summary_by_host_by_event_name:
Stage events per host name and event name
events_stages_summary_by_thread_by_event_name:
Stage waits per thread and event name
events_stages_summary_by_user_by_event_name:
Stage events per user name and event name
events_stages_summary_global_by_event_name:
Stage waits per event name
events_statements_summary_by_account_by_event_name:
Statement events per account and event name
events_statements_summary_by_digest:
Statement events per schema and digest value
events_statements_summary_by_host_by_event_name:
Statement events per host name and event name
events_statements_summary_by_thread_by_event_name:
Statement events per thread and event name
events_statements_summary_by_user_by_event_name:
Statement events per user name and event name
events_statements_summary_global_by_event_name:
Statement events per event name
objects_summary_global_by_type:
Object summaries
file_summary_by_event_name:
File events per event name
file_summary_by_instance: File
events per file instance
table_io_waits_summary_by_index_usage:
Table I/O waits per index
table_io_waits_summary_by_table:
Table I/O waits per table
table_lock_waits_summary_by_table:
Table lock waits per table
socket_summary_by_instance:
Socket waits and I/O per instance
socket_summary_by_event_name:
Socket waits and I/O per event name
Each summary table has grouping columns that determine how to group the data to be aggregated, and summary columns that contain the aggregated values. Tables that summarize events in similar ways often have similar sets of summary columns and differ only in the grouping columns used to determine how events are aggregated.
Summary tables can be truncated with
TRUNCATE TABLE. Generally, the
effect is to reset the summary columns to 0 or
NULL, not to remove rows. This enables you to
clear collected values and restart aggregation. That might be
useful, for example, after you have made a runtime configuration
change. Exceptions to this truncation behavior are noted in
individual summary table sections.
The Performance Schema maintains tables for collecting current and recent wait events, and aggregates that information in summary tables. Section 22.12.4, “Performance Schema Wait Event Tables” describes the events on which wait summaries are based. See that discussion for information about the content of wait events, the current and recent wait event tables, and how to control wait event collection, which is disabled by default.
Example wait event summary information:
mysql>SELECT *FROM performance_schema.events_waits_summary_global_by_event_name\G... *************************** 6. row *************************** EVENT_NAME: wait/synch/mutex/sql/BINARY_LOG::LOCK_index COUNT_STAR: 8 SUM_TIMER_WAIT: 2119302 MIN_TIMER_WAIT: 196092 AVG_TIMER_WAIT: 264912 MAX_TIMER_WAIT: 569421 ... *************************** 9. row *************************** EVENT_NAME: wait/synch/mutex/sql/hash_filo::lock COUNT_STAR: 69 SUM_TIMER_WAIT: 16848828 MIN_TIMER_WAIT: 0 AVG_TIMER_WAIT: 244185 MAX_TIMER_WAIT: 735345 ...
Each wait event summary table has one or more grouping columns
to indicate how the table aggregates events. Event names refer
to names of event instruments in the
setup_instruments table:
events_waits_summary_by_account_by_event_name
has EVENT_NAME,
USER, and HOST
columns. Each row summarizes events for a given account
(user and host combination) and event name.
events_waits_summary_by_host_by_event_name
has EVENT_NAME and
HOST columns. Each row summarizes
events for a given host and event name.
events_waits_summary_by_instance
has EVENT_NAME and
OBJECT_INSTANCE_BEGIN columns. Each row
summarizes events for a given event name and object. If an
instrument is used to create multiple instances, each
instance has a unique
OBJECT_INSTANCE_BEGIN value and is
summarized separately in this table.
events_waits_summary_by_thread_by_event_name
has THREAD_ID and
EVENT_NAME columns. Each row summarizes
events for a given thread and event name.
events_waits_summary_by_user_by_event_name
has EVENT_NAME and
USER columns. Each row summarizes
events for a given user and event name.
events_waits_summary_global_by_event_name
has an EVENT_NAME column. Each row
summarizes events for a given event name. An instrument
might be used to create multiple instances of the
instrumented object. For example, if there is an
instrument for a mutex that is created for each
connection, there are as many instances as there are
connections. The summary row for the instrument summarizes
over all these instances.
Each wait event summary table has these summary columns containing aggregated values:
COUNT_STAR
The number of summarized events. This value includes all events, whether timed or nontimed.
SUM_TIMER_WAIT
The total wait time of the summarized timed events. This
value is calculated only for timed events because nontimed
events have a wait time of NULL. The
same is true for the other
xxx_TIMER_WAIT
MIN_TIMER_WAIT
The minimum wait time of the summarized timed events.
AVG_TIMER_WAIT
The average wait time of the summarized timed events.
MAX_TIMER_WAIT
The maximum wait time of the summarized timed events.
TRUNCATE TABLE is permitted for
wait summary tables. It has these effects:
For summary tables not aggregated by account, host, or user, truncation resets the summary columns to zero rather than removing rows.
For summary tables aggregated by account, host, or user, truncation removes rows for accounts, hosts, or users with no connections, and resets the summary columns to zero for the remaining rows.
In addition, each wait summary table that is aggregated by
account, host, user, or thread is implicitly truncated by
truncation of the connection table on which it depends, or
truncation of
events_waits_summary_global_by_event_name.
For details, see
Section 22.12.7, “Performance Schema Connection Tables”.
The Performance Schema maintains tables for collecting current and recent stage events, and aggregates that information in summary tables. Section 22.12.5, “Performance Schema Stage Event Tables” describes the events on which stage summaries are based. See that discussion for information about the content of stage events, the current and historical stage event tables, and how to control stage event collection, which is disabled by default.
Example stage event summary information:
mysql>SELECT *FROM performance_schema.events_stages_summary_global_by_event_name\G... *************************** 5. row *************************** EVENT_NAME: stage/sql/checking permissions COUNT_STAR: 57 SUM_TIMER_WAIT: 26501888880 MIN_TIMER_WAIT: 7317456 AVG_TIMER_WAIT: 464945295 MAX_TIMER_WAIT: 12858936792 ... *************************** 9. row *************************** EVENT_NAME: stage/sql/closing tables COUNT_STAR: 37 SUM_TIMER_WAIT: 662606568 MIN_TIMER_WAIT: 1593864 AVG_TIMER_WAIT: 17907891 MAX_TIMER_WAIT: 437977248 ...
Each stage summary table has one or more grouping columns to
indicate how the table aggregates events. Event names refer to
names of event instruments in the
setup_instruments table:
events_stages_summary_by_account_by_event_name
has EVENT_NAME,
USER, and HOST
columns. Each row summarizes events for a given account
(user and host combination) and event name.
events_stages_summary_by_host_by_event_name
has EVENT_NAME and
HOST columns. Each row summarizes
events for a given host and event name.
events_stages_summary_by_thread_by_event_name
has THREAD_ID and
EVENT_NAME columns. Each row summarizes
events for a given thread and event name.
events_stages_summary_by_user_by_event_name
has EVENT_NAME and
USER columns. Each row summarizes
events for a given user and event name.
events_stages_summary_global_by_event_name
has an EVENT_NAME column. Each row
summarizes events for a given event name.
Each stage summary table has these summary columns containing
aggregated values: COUNT_STAR,
SUM_TIMER_WAIT,
MIN_TIMER_WAIT,
AVG_TIMER_WAIT, and
MAX_TIMER_WAIT. These columns are analogous
to the columns of the same names in the wait event summary
tables (see Section 22.12.9.1, “Wait Event Summary Tables”), except
that the stage summary tables aggregate events from
events_stages_current rather than
events_waits_current.
TRUNCATE TABLE is permitted for
stage summary tables. It has these effects:
For summary tables not aggregated by account, host, or user, truncation resets the summary columns to zero rather than removing rows.
For summary tables aggregated by account, host, or user, truncation removes rows for accounts, hosts, or users with no connections, and resets the summary columns to zero for the remaining rows.
In addition, each stage summary table that is aggregated by
account, host, user, or thread is implicitly truncated by
truncation of the connection table on which it depends, or
truncation of
events_stages_summary_global_by_event_name.
For details, see
Section 22.12.7, “Performance Schema Connection Tables”.
The Performance Schema maintains tables for collecting current and recent statement events, and aggregates that information in summary tables. Section 22.12.6, “Performance Schema Statement Event Tables” describes the events on which statement summaries are based. See that discussion for information about the content of statement events, the current and historical statement event tables, and how to control statement event collection, which is partially disabled by default.
Example statement event summary information:
mysql>SELECT *FROM performance_schema.events_statements_summary_global_by_event_name\G*************************** 1. row *************************** EVENT_NAME: statement/sql/select COUNT_STAR: 25 SUM_TIMER_WAIT: 1535983999000 MIN_TIMER_WAIT: 209823000 AVG_TIMER_WAIT: 61439359000 MAX_TIMER_WAIT: 1363397650000 SUM_LOCK_TIME: 20186000000 SUM_ERRORS: 0 SUM_WARNINGS: 0 SUM_ROWS_AFFECTED: 0 SUM_ROWS_SENT: 388 SUM_ROWS_EXAMINED: 370 SUM_CREATED_TMP_DISK_TABLES: 0 SUM_CREATED_TMP_TABLES: 0 SUM_SELECT_FULL_JOIN: 0 SUM_SELECT_FULL_RANGE_JOIN: 0 SUM_SELECT_RANGE: 0 SUM_SELECT_RANGE_CHECK: 0 SUM_SELECT_SCAN: 6 SUM_SORT_MERGE_PASSES: 0 SUM_SORT_RANGE: 0 SUM_SORT_ROWS: 0 SUM_SORT_SCAN: 0 SUM_NO_INDEX_USED: 6 SUM_NO_GOOD_INDEX_USED: 0 ...
Each statement summary table has one or more grouping columns
to indicate how the table aggregates events. Event names refer
to names of event instruments in the
setup_instruments table:
events_statements_summary_by_account_by_event_name
has EVENT_NAME,
USER, and HOST
columns. Each row summarizes events for a given account
(user and host combination) and event name.
events_statements_summary_by_digest
has SCHEMA_NAME and
DIGEST columns. Each row summarizes
events per schema and digest value. (The
DIGEST_TEXT column contains the
corresponding normalized statement digest text, but is
neither a grouping nor a summary column.)
The maximum number of rows in the table is autosized at
server startup. To set this maximum explicitly, set the
performance_schema_digests_size
system variable at server startup.
events_statements_summary_by_host_by_event_name
has EVENT_NAME and
HOST columns. Each row summarizes
events for a given host and event name.
events_statements_summary_by_thread_by_event_name
has THREAD_ID and
EVENT_NAME columns. Each row summarizes
events for a given thread and event name.
events_statements_summary_by_user_by_event_name
has EVENT_NAME and
USER columns. Each row summarizes
events for a given user and event name.
events_statements_summary_global_by_event_name
has an EVENT_NAME column. Each row
summarizes events for a given event name.
Each statement summary table has these summary columns containing aggregated values:
COUNT_STAR,
SUM_TIMER_WAIT,
MIN_TIMER_WAIT,
AVG_TIMER_WAIT,
MAX_TIMER_WAIT
These columns are analogous to the columns of the same
names in the wait event summary tables (see
Section 22.12.9.1, “Wait Event Summary Tables”), except that the
statement summary tables aggregate events from
events_statements_current
rather than
events_waits_current.
SUM_
xxx
The aggregate of the corresponding
xxx column in the
events_statements_current
table. For example, the SUM_LOCK_TIME
and SUM_ERRORS columns in statement
summary tables are the aggregates of the
LOCK_TIME and ERRORS
columns in
events_statements_current
table.
The
events_statements_summary_by_digest
table has these additional summary columns:
FIRST_SEEN,
LAST_SEEN
Timestamps indicating when statements with the given digest value were first seen and most recently seen.
TRUNCATE TABLE is permitted for
statement summary tables. It has these effects:
For
events_statements_summary_by_digest,
it removes the rows.
For other summary tables not aggregated by account, host, or user, truncation resets the summary columns to zero rather than removing rows.
For other summary tables aggregated by account, host, or user, truncation removes rows for accounts, hosts, or users with no connections, and resets the summary columns to zero for the remaining rows.
In addition, each statement summary table that is aggregated
by account, host, user, or thread is implicitly truncated by
truncation of the connection table on which it depends, or
truncation of
events_statements_summary_global_by_event_name.
For details, see
Section 22.12.7, “Performance Schema Connection Tables”.
If the statements_digest consumer is
enabled, aggregation into
events_statements_summary_by_digest
occurs as follows when a statement completes. Aggregation is
based on the DIGEST value computed for
the statement.
If a
events_statements_summary_by_digest
row already exists with the digest value for the
statement that just completed, statistics for the
statement are aggregated to that row. The
LAST_SEEN column is updated to the
current time.
If no row has the digest value for the statement that
just completed, and the table is not full, a new row is
created for the statement. The
FIRST_SEEN and
LAST_SEEN columns are initialized
with the current time.
If no row has the statement digest value for the
statement that just completed, and the table is full,
the statistics for the statement that just completed are
added to a special “catch-all” row with
DIGEST = NULL,
which is created if necessary. If the row is created,
the FIRST_SEEN and
LAST_SEEN columns are initialized
with the current time. Otherwise, the
LAST_SEEN column is updated with the
current time.
The row with DIGEST =
NULL is maintained because Performance
Schema tables have a maximum size due to memory constraints.
The DIGEST = NULL row
permits digests that do not match other rows to be counted
even if the summary table is full, using a common
“other” bucket. This row helps you estimate
whether the digest summary is representative:
A DIGEST = NULL
row that has a COUNT_STAR value that
represents 5% of all digests shows that the digest
summary table is very representative; the other rows
cover 95% of the statements seen.
A DIGEST = NULL
row that has a COUNT_STAR value that
represents 50% of all digests shows that the digest
summary table is not very representative; the other rows
cover only half the statements seen. Most likely the DBA
should increase the maximum table size so that more of
the rows counted in the DIGEST =
NULL row would be counted using more
specific rows instead. To do this, set the
performance_schema_digests_size
system variable to a larger value at server startup. The
default size is 200.
The Performance Schema maintains the
objects_summary_global_by_type
table for aggregating object wait events.
Example object wait event summary information:
mysql> SELECT * FROM performance_schema.objects_summary_global_by_type\G
...
*************************** 3. row ***************************
OBJECT_TYPE: TABLE
OBJECT_SCHEMA: test
OBJECT_NAME: t
COUNT_STAR: 3
SUM_TIMER_WAIT: 263126976
MIN_TIMER_WAIT: 1522272
AVG_TIMER_WAIT: 87708678
MAX_TIMER_WAIT: 258428280
...
*************************** 10. row ***************************
OBJECT_TYPE: TABLE
OBJECT_SCHEMA: mysql
OBJECT_NAME: user
COUNT_STAR: 14
SUM_TIMER_WAIT: 365567592
MIN_TIMER_WAIT: 1141704
AVG_TIMER_WAIT: 26111769
MAX_TIMER_WAIT: 334783032
...
The
objects_summary_global_by_type
table has these grouping columns to indicate how the table
aggregates events: OBJECT_TYPE,
OBJECT_SCHEMA, and
OBJECT_NAME. Each row summarizes events for
the given object.
objects_summary_global_by_type
has the same summary columns as the
events_waits_summary_by_
tables. See Section 22.12.9.1, “Wait Event Summary Tables”.
xxx
TRUNCATE TABLE is permitted for
the object summary table. It resets the summary columns to
zero rather than removing rows.
The Performance Schema maintains file I/O summary tables that aggregate information about I/O operations.
Example file I/O event summary information:
mysql>SELECT * FROM performance_schema.file_summary_by_event_name\G... *************************** 2. row *************************** EVENT_NAME: wait/io/file/sql/binlog COUNT_STAR: 31 SUM_TIMER_WAIT: 8243784888 MIN_TIMER_WAIT: 0 AVG_TIMER_WAIT: 265928484 MAX_TIMER_WAIT: 6490658832 ... mysql>SELECT * FROM performance_schema.file_summary_by_instance\G... *************************** 2. row *************************** FILE_NAME: /var/mysql/share/english/errmsg.sys EVENT_NAME: wait/io/file/sql/ERRMSG EVENT_NAME: wait/io/file/sql/ERRMSG OBJECT_INSTANCE_BEGIN: 4686193384 COUNT_STAR: 5 SUM_TIMER_WAIT: 13990154448 MIN_TIMER_WAIT: 26349624 AVG_TIMER_WAIT: 2798030607 MAX_TIMER_WAIT: 8150662536 ...
Each file I/O summary table has one or more grouping columns
to indicate how the table aggregates events. Event names refer
to names of event instruments in the
setup_instruments table:
file_summary_by_event_name
has an EVENT_NAME column. Each row
summarizes events for a given event name.
file_summary_by_instance has
FILE_NAME,
EVENT_NAME, and
OBJECT_INSTANCE_BEGIN columns. Each row
summarizes events for a given file and event name.
Each file I/O summary table has the following summary columns containing aggregated values. Some columns are more general and have values that are the same as the sum of the values of more fine-grained columns. In this way, aggregations at higher levels are available directly without the need for user-defined views that sum lower-level columns.
COUNT_STAR,
SUM_TIMER_WAIT,
MIN_TIMER_WAIT,
AVG_TIMER_WAIT,
MAX_TIMER_WAIT
These columns aggregate all I/O operations.
COUNT_READ,
SUM_TIMER_READ,
MIN_TIMER_READ,
AVG_TIMER_READ,
MAX_TIMER_READ,
SUM_NUMBER_OF_BYTES_READ
These columns aggregate all read operations, including
FGETS, FGETC,
FREAD, and READ.
COUNT_WRITE,
SUM_TIMER_WRITE,
MIN_TIMER_WRITE,
AVG_TIMER_WRITE,
MAX_TIMER_WRITE,
SUM_NUMBER_OF_BYTES_WRITE
These columns aggregate all write operations, including
FPUTS, FPUTC,
FPRINTF, VFPRINTF,
FWRITE, and PWRITE.
COUNT_MISC,
SUM_TIMER_MISC,
MIN_TIMER_MISC,
AVG_TIMER_MISC,
MAX_TIMER_MISC
These columns aggregate all other I/O operations,
including CREATE,
DELETE, OPEN,
CLOSE, STREAM_OPEN,
STREAM_CLOSE, SEEK,
TELL, FLUSH,
STAT, FSTAT,
CHSIZE, RENAME, and
SYNC. There are no byte counts for
these operations.
TRUNCATE TABLE is permitted for
file I/O summary tables. It resets the summary columns to zero
rather than removing rows.
The MySQL server uses several techniques to avoid I/O operations by caching information read from files, so it is possible that statements you might expect to result in I/O events will not. You may be able to ensure that I/O does occur by flushing caches or restarting the server to reset its state.
The following sections describe the table I/O and lock wait summary tables:
table_io_waits_summary_by_index_usage:
Table I/O waits per index
table_io_waits_summary_by_table:
Table I/O waits per table
table_lock_waits_summary_by_table:
Table lock waits per table
The
table_io_waits_summary_by_table
table aggregates all table I/O wait events, as generated by
the wait/io/table/sql/handler instrument.
The grouping is by table.
The
table_io_waits_summary_by_table
table has these grouping columns to indicate how the table
aggregates events: OBJECT_TYPE,
OBJECT_SCHEMA, and
OBJECT_NAME. These columns have the same
meaning as in the
events_waits_current table.
They identify the table to which the row applies.
table_io_waits_summary_by_table
has the following summary columns containing aggregated
values. As indicated in the column descriptions, some
columns are more general and have values that are the same
as the sum of the values of more fine-grained columns. For
example, columns that aggregate all writes hold the sum of
the corresponding columns that aggregate inserts, updates,
and deletes. In this way, aggregations at higher levels are
available directly without the need for user-defined views
that sum lower-level columns.
COUNT_STAR,
SUM_TIMER_WAIT,
MIN_TIMER_WAIT,
AVG_TIMER_WAIT,
MAX_TIMER_WAIT
These columns aggregate all I/O operations. They are the
same as the sum of the corresponding
xxx_READxxx_WRITE
COUNT_READ,
SUM_TIMER_READ,
MIN_TIMER_READ,
AVG_TIMER_READ,
MAX_TIMER_READ
These columns aggregate all read operations. They are
the same as the sum of the corresponding
xxx_FETCH
COUNT_WRITE,
SUM_TIMER_WRITE,
MIN_TIMER_WRITE,
AVG_TIMER_WRITE,
MAX_TIMER_WRITE
These columns aggregate all write operations. They are
the same as the sum of the corresponding
xxx_INSERTxxx_UPDATExxx_DELETE
COUNT_FETCH,
SUM_TIMER_FETCH,
MIN_TIMER_FETCH,
AVG_TIMER_FETCH,
MAX_TIMER_FETCH
These columns aggregate all fetch operations.
COUNT_INSERT,
SUM_TIMER_INSERT,
MIN_TIMER_INSERT,
AVG_TIMER_INSERT,
MAX_TIMER_INSERT
These columns aggregate all insert operations.
COUNT_UPDATE,
SUM_TIMER_UPDATE,
MIN_TIMER_UPDATE,
AVG_TIMER_UPDATE,
MAX_TIMER_UPDATE
These columns aggregate all update operations.
COUNT_DELETE,
SUM_TIMER_DELETE,
MIN_TIMER_DELETE,
AVG_TIMER_DELETE,
MAX_TIMER_DELETE
These columns aggregate all delete operations.
TRUNCATE TABLE is permitted
for table I/O summary tables. It resets the summary columns
to zero rather than removing rows. Truncating this table
also truncates the
table_io_waits_summary_by_index_usage
table.
The
table_io_waits_summary_by_index_usage
table aggregates all table index I/O wait events, as
generated by the
wait/io/table/sql/handler instrument. The
grouping is by table index.
The columns of
table_io_waits_summary_by_index_usage
are nearly identical to
table_io_waits_summary_by_table.
The only difference is the additional group column,
INDEX_NAME, which corresponds to the name
of the index that was used when the table I/O wait event was
recorded:
A value of PRIMARY indicates that
table I/O used the primary index.
A value of NULL means that table I/O
used no index.
Inserts are counted against INDEX_NAME =
NULL.
TRUNCATE TABLE is permitted
for table I/O summary tables. It resets the summary columns
to zero rather than removing rows. This table is also
truncated by truncation of the
table_io_waits_summary_by_table
table. A DDL operation that changes the index structure of a
table may cause the per-index statistics to be reset.
The
table_lock_waits_summary_by_table
table aggregates all table lock wait events, as generated by
the wait/lock/table/sql/handler
instrument. The grouping is by table.
This table contains information about internal and external locks:
An internal lock corresponds to a lock in the SQL layer.
This is currently implemented by a call to
thr_lock(). In event rows, these
locks are distinguished by the
OPERATION column, which has one of
these values:
read normal read with shared locks read high priority read no insert write allow write write concurrent insert write delayed write low priority write normal
An external lock corresponds to a lock in the storage
engine layer. This is currently implemented by a call to
handler::external_lock(). In event
rows, these locks are distinguished by the
OPERATION column, which has one of
these values:
read external write external
The
table_lock_waits_summary_by_table
table has these grouping columns to indicate how the table
aggregates events: OBJECT_TYPE,
OBJECT_SCHEMA, and
OBJECT_NAME. These columns have the same
meaning as in the
events_waits_current table.
They identify the table to which the row applies.
table_lock_waits_summary_by_table
has the following summary columns containing aggregated
values. As indicated in the column descriptions, some
columns are more general and have values that are the same
as the sum of the values of more fine-grained columns. For
example, columns that aggregate all locks hold the sum of
the corresponding columns that aggregate read and write
locks. In this way, aggregations at higher levels are
available directly without the need for user-defined views
that sum lower-level columns.
COUNT_STAR,
SUM_TIMER_WAIT,
MIN_TIMER_WAIT,
AVG_TIMER_WAIT,
MAX_TIMER_WAIT
These columns aggregate all lock operations. They are
the same as the sum of the corresponding
xxx_READxxx_WRITE
COUNT_READ,
SUM_TIMER_READ,
MIN_TIMER_READ,
AVG_TIMER_READ,
MAX_TIMER_READ
These columns aggregate all read-lock operations. They
are the same as the sum of the corresponding
xxx_READ_NORMALxxx_READ_WITH_SHARED_LOCKSxxx_READ_HIGH_PRIORITYxxx_READ_NO_INSERT
COUNT_WRITE,
SUM_TIMER_WRITE,
MIN_TIMER_WRITE,
AVG_TIMER_WRITE,
MAX_TIMER_WRITE
These columns aggregate all write-lock operations. They
are the same as the sum of the corresponding
xxx_WRITE_ALLOW_WRITExxx_WRITE_CONCURRENT_INSERTxxx_WRITE_DELAYEDxxx_WRITE_LOW_PRIORITYxxx_WRITE_NORMAL
COUNT_READ_NORMAL,
SUM_TIMER_READ_NORMAL,
MIN_TIMER_READ_NORMAL,
AVG_TIMER_READ_NORMAL,
MAX_TIMER_READ_NORMAL
These columns aggregate internal read locks.
COUNT_READ_WITH_SHARED_LOCKS,
SUM_TIMER_READ_WITH_SHARED_LOCKS,
MIN_TIMER_READ_WITH_SHARED_LOCKS,
AVG_TIMER_READ_WITH_SHARED_LOCKS,
MAX_TIMER_READ_WITH_SHARED_LOCKS
These columns aggregate internal read locks.
COUNT_READ_HIGH_PRIORITY,
SUM_TIMER_READ_HIGH_PRIORITY,
MIN_TIMER_READ_HIGH_PRIORITY,
AVG_TIMER_READ_HIGH_PRIORITY,
MAX_TIMER_READ_HIGH_PRIORITY
These columns aggregate internal read locks.
COUNT_READ_NO_INSERT,
SUM_TIMER_READ_NO_INSERT,
MIN_TIMER_READ_NO_INSERT,
AVG_TIMER_READ_NO_INSERT,
MAX_TIMER_READ_NO_INSERT
These columns aggregate internal read locks.
COUNT_READ_EXTERNAL,
SUM_TIMER_READ_EXTERNAL,
MIN_TIMER_READ_EXTERNAL,
AVG_TIMER_READ_EXTERNAL,
MAX_TIMER_READ_EXTERNAL
These columns aggregate external read locks.
COUNT_WRITE_ALLOW_WRITE,
SUM_TIMER_WRITE_ALLOW_WRITE,
MIN_TIMER_WRITE_ALLOW_WRITE,
AVG_TIMER_WRITE_ALLOW_WRITE,
MAX_TIMER_WRITE_ALLOW_WRITE
These columns aggregate internal write locks.
COUNT_WRITE_CONCURRENT_INSERT,
SUM_TIMER_WRITE_CONCURRENT_INSERT,
MIN_TIMER_WRITE_CONCURRENT_INSERT,
AVG_TIMER_WRITE_CONCURRENT_INSERT,
MAX_TIMER_WRITE_CONCURRENT_INSERT
These columns aggregate internal write locks.
COUNT_WRITE_DELAYED,
SUM_TIMER_WRITE_DELAYED,
MIN_TIMER_WRITE_DELAYED,
AVG_TIMER_WRITE_DELAYED,
MAX_TIMER_WRITE_DELAYED
These columns aggregate internal write locks.
DELAYED inserts are deprecated, so
these columns will be removed in a future release.
COUNT_WRITE_LOW_PRIORITY,
SUM_TIMER_WRITE_LOW_PRIORITY,
MIN_TIMER_WRITE_LOW_PRIORITY,
AVG_TIMER_WRITE_LOW_PRIORITY,
MAX_TIMER_WRITE_LOW_PRIORITY
These columns aggregate internal write locks.
COUNT_WRITE_NORMAL,
SUM_TIMER_WRITE_NORMAL,
MIN_TIMER_WRITE_NORMAL,
AVG_TIMER_WRITE_NORMAL,
MAX_TIMER_WRITE_NORMAL
These columns aggregate internal write locks.
COUNT_WRITE_EXTERNAL,
SUM_TIMER_WRITE_EXTERNAL,
MIN_TIMER_WRITE_EXTERNAL,
AVG_TIMER_WRITE_EXTERNAL,
MAX_TIMER_WRITE_EXTERNAL
These columns aggregate external write locks.
TRUNCATE TABLE is permitted
for table lock summary tables. It resets the summary columns
to zero rather than removing rows.
The Performance Schema maintains socket summary tables, which aggregate timer and byte count information for socket operations:
socket_summary_by_event_name:
Aggregate timer and byte count statistics generated by the
wait/io/socket/* instruments for all
socket I/O operations, per socket instrument.
socket_summary_by_instance:
Aggregate timer and byte count statistics generated by the
wait/io/socket/* instruments for all
socket I/O operations, per socket instance. When a
connection terminates, the row in
socket_summary_by_instance
corresponding to it is deleted.
The socket summary tables do not aggregate waits generated by
idle events while sockets are waiting for
the next request from the client. For idle
event aggregations, use the wait-event summary tables; see
Section 22.12.9.1, “Wait Event Summary Tables”.
Each socket summary table has one or more grouping columns to
indicate how the table aggregates events. Event names refer to
names of event instruments in the
setup_instruments table:
socket_summary_by_event_name
has an EVENT_NAME column. Each row
summarizes events for a given event name.
socket_summary_by_instance
has an OBJECT_INSTANCE_BEGIN column.
Each row summarizes events for a given object.
Each socket summary table has these summary columns containing aggregated values:
COUNT_STAR,
SUM_TIMER_WAIT,
MIN_TIMER_WAIT,
AVG_TIMER_WAIT,
MAX_TIMER_WAIT
These columns aggregate all operations.
COUNT_READ,
SUM_TIMER_READ,
MIN_TIMER_READ,
AVG_TIMER_READ,
MAX_TIMER_READ,
SUM_NUMBER_OF_BYTES_READ
These columns aggregate all receive operations
(RECV, RECVFROM, and
RECVMSG).
COUNT_WRITE,
SUM_TIMER_WRITE,
MIN_TIMER_WRITE,
AVG_TIMER_WRITE,
MAX_TIMER_WRITE,
SUM_NUMBER_OF_BYTES_WRITE
These columns aggregate all send operations
(SEND, SENDTO, and
SENDMSG).
COUNT_MISC,
SUM_TIMER_MISC,
MIN_TIMER_MISC,
AVG_TIMER_MISC,
MAX_TIMER_MISC
These columns aggregate all other socket operations, such
as CONNECT, LISTEN,
ACCEPT, CLOSE, and
SHUTDOWN. There are no byte counts for
these operations.
The socket_summary_by_instance
table also has an EVENT_NAME column that
indicates the class of the socket:
client_connection,
server_tcpip_socket,
server_unix_socket. This column can be
grouped on to isolate, for example, client activity from that
of the server listening sockets.
TRUNCATE TABLE is permitted for
socket summary tables. Except for
events_statements_summary_by_digest,
tt resets the summary columns to zero rather than removing
rows.
The following sections describe tables that do not fall into the table categories discussed in the preceding sections:
host_cache: Information from
the internal host cache
performance_timers: Which event
timers are available
threads: Information about
server threads
The host_cache table provides
access to the contents of the host cache, which contains
client host name and IP address information and is used to
avoid Domain Name System (DNS) lookups. The
host_cache_size system
variable controls the size of the host cache, as well as the
size of the host_cache table that
exposes the cache contents. For operational and configuration
information about the host cache, see
Section 8.12.5.2, “DNS Lookup Optimization and the Host Cache”.
Because the host_cache table
exposes the contents of the host cache, it can be examined
using SELECT statements. This
may help you diagnose the causes of connection problems. The
Performance Schema must be enabled or this table is empty.
The host_cache table has these
columns:
IP
The IP address of the client that connected to the server, expressed as a string.
HOST
The resolved DNS host name for that client IP, or
NULL if the name is unknown.
HOST_VALIDATED
Whether the IP-to-host name-to-IP DNS resolution was
performed successfully for the client IP. If
HOST_VALIDATED is
YES, the HOST column
is used as the host name corresponding to the IP so that
additional calls to DNS can be avoided. While
HOST_VALIDATED is
NO, DNS resolution is attempted for
each connection attempt, until it eventually completes
with either a valid result or a permanent error. This
information enables the server to avoid caching bad or
missing host names during temporary DNS failures, which
would negatively affect clients forever.
SUM_CONNECT_ERRORS
The number of connection errors that are deemed
“blocking” (assessed against the
max_connect_errors system
variable). Only protocol handshake errors are counted, and
only for hosts that passed validation
(HOST_VALIDATED = YES).
Once SUM_CONNECT_ERRORS for a given
host reaches the value of
max_connect_errors, new
connections from that host are blocked. The
SUM_CONNECT_ERRORS value can exceed the
max_connect_errors value
because multiple connection attempts from a host can occur
simultaneously while the host is not blocked. Any or all
of them can fail, independently incrementing
SUM_CONNECT_ERRORS, possibly beyond the
value of
max_connect_errors.
Suppose that
max_connect_errors is 200
and SUM_CONNECT_ERRORS for a given host
is 199. If 10 clients attempt to connect from that host
simultaneously, none of them are blocked because
SUM_CONNECT_ERRORS has not reached 200.
If blocking errors occur for five of the clients,
SUM_CONNECT_ERRORS is increased by one
for each client, for a resulting
SUM_CONNECT_ERRORS value of 204. The
other five clients succeed and are not blocked because the
value of SUM_CONNECT_ERRORS when their
connection attempts began had not reached 200. New
connections from the host that begin after
SUM_CONNECT_ERRORS reaches 200 are
blocked.
COUNT_HOST_BLOCKED_ERRORS
The number of connections that were blocked because
SUM_CONNECT_ERRORS exceeded the value
of the max_connect_errors
system variable.
COUNT_NAMEINFO_TRANSIENT_ERRORS
The number of transient errors during IP-to-host name DNS resolution.
COUNT_NAMEINFO_PERMANENT_ERRORS
The number of permanent errors during IP-to-host name DNS resolution.
COUNT_FORMAT_ERRORS
The number of host name format errors. MySQL does not
perform matching of Host column values
in the mysql.user system table against
host names for which one or more of the initial components
of the name are entirely numeric, such as
1.2.example.com. The client IP address
is used instead. For the rationale why this type of
matching does not occur, see
Section 6.2.4, “Specifying Account Names”.
COUNT_ADDRINFO_TRANSIENT_ERRORS
The number of transient errors during host name-to-IP reverse DNS resolution.
COUNT_ADDRINFO_PERMANENT_ERRORS
The number of permanent errors during host name-to-IP reverse DNS resolution.
COUNT_FCRDNS_ERRORS
The number of forward-confirmed reverse DNS errors. These errors occur when IP-to-host name-to-IP DNS resolution produces an IP address that does not match the client originating IP address.
COUNT_HOST_ACL_ERRORS
The number of errors that occur because no users are
permitted to connect from the client host. In such cases,
the server returns
ER_HOST_NOT_PRIVILEGED and
does not even ask for a user name or password.
COUNT_NO_AUTH_PLUGIN_ERRORS
The number of errors due to requests for an unavailable authentication plugin. A plugin can be unavailable if, for example, it was never loaded or a load attempt failed.
COUNT_AUTH_PLUGIN_ERRORS
The number of errors reported by authentication plugins.
An authentication plugin can report different error codes
to indicate the root cause of a failure. Depending on the
type of error, one of these columns is incremented:
COUNT_AUTHENTICATION_ERRORS,
COUNT_AUTH_PLUGIN_ERRORS,
COUNT_HANDSHAKE_ERRORS. New return
codes are an optional extension to the existing plugin
API. Unknown or unexpected plugin errors are counted in
the COUNT_AUTH_PLUGIN_ERRORS column.
COUNT_HANDSHAKE_ERRORS
The number of errors detected at the wire protocol level.
COUNT_PROXY_USER_ERRORS
The number of errors detected when proxy user A is proxied to another user B who does not exist.
COUNT_PROXY_USER_ACL_ERRORS
The number of errors detected when proxy user A is proxied
to another user B who does exist but for whom A does not
have the PROXY privilege.
COUNT_AUTHENTICATION_ERRORS
The number of errors caused by failed authentication.
COUNT_SSL_ERRORS
The number of errors due to SSL problems.
COUNT_MAX_USER_CONNECTIONS_ERRORS
The number of errors caused by exceeding per-user connection quotas. See Section 6.2.13, “Setting Account Resource Limits”.
COUNT_MAX_USER_CONNECTIONS_PER_HOUR_ERRORS
The number of errors caused by exceeding per-user connections-per-hour quotas. See Section 6.2.13, “Setting Account Resource Limits”.
COUNT_DEFAULT_DATABASE_ERRORS
The number of errors related to the default database. For example, the database does not exist or the user has no privileges to access it.
COUNT_INIT_CONNECT_ERRORS
The number of errors caused by execution failures of
statements in the
init_connect system
variable value.
COUNT_LOCAL_ERRORS
The number of errors local to the server implementation and not related to the network, authentication, or authorization. For example, out-of-memory conditions fall into this category.
COUNT_UNKNOWN_ERRORS
The number of other, unknown errors not accounted for by
other columns in this table. This column is reserved for
future use, in case new error conditions must be reported,
and if preserving the backward compatibility and structure
of the host_cache table is
required.
FIRST_SEEN
The timestamp of the first connection attempt seen from
the client in the IP column.
LAST_SEEN
The timestamp of the most recent connection attempt seen
from the client in the IP column.
FIRST_ERROR_SEEN
The timestamp of the first error seen from the client in
the IP column.
LAST_ERROR_SEEN
The timestamp of the most recent error seen from the
client in the IP column.
The FLUSH HOSTS statement,
TRUNCATE TABLE
host_cache statement, and mysqladmin
flush-hosts command have the same effect: They clear
the host cache, remove all rows from the
host_cache table that exposes the
cache contents, and unblock any blocked hosts (see
Section B.4.2.6, “Host 'host_name' is blocked”). FLUSH
HOSTS and mysqladmin flush-hosts
require the RELOAD privilege.
TRUNCATE TABLE requires the
DROP privilege for the
host_cache table.
The performance_timers table
shows which event timers are available:
mysql> SELECT * FROM performance_schema.performance_timers;
+-------------+-----------------+------------------+----------------+
| TIMER_NAME | TIMER_FREQUENCY | TIMER_RESOLUTION | TIMER_OVERHEAD |
+-------------+-----------------+------------------+----------------+
| CYCLE | 2389029850 | 1 | 72 |
| NANOSECOND | 1000000000 | 1 | 112 |
| MICROSECOND | 1000000 | 1 | 136 |
| MILLISECOND | 1036 | 1 | 168 |
| TICK | 105 | 1 | 2416 |
+-------------+-----------------+------------------+----------------+
If the values associated with a given timer name are
NULL, that timer is not supported on your
platform. The rows that do not contain NULL
indicate which timers you can use in
setup_timers. For an explanation
of how event timing occurs, see
Section 22.4.1, “Performance Schema Event Timing”.
The performance_timers table has
these columns:
TIMER_NAME
The name by which to refer to the timer when configuring
the setup_timers table.
TIMER_FREQUENCY
The number of timer units per second. For a cycle timer,
the frequency is generally related to the CPU speed. For
example, on a system with a 2.4GHz processor, the
CYCLE may be close to 2400000000.
TIMER_RESOLUTION
Indicates the number of timer units by which timer values increase. If a timer has a resolution of 10, its value increases by 10 each time.
TIMER_OVERHEAD
The minimal number of cycles of overhead to obtain one timing with the given timer. The Performance Schema determines this value by invoking the timer 20 times during initialization and picking the smallest value. The total overhead really is twice this amount because the instrumentation invokes the timer at the start and end of each event. The timer code is called only for timed events, so this overhead does not apply for nontimed events.
TRUNCATE TABLE is not permitted
for the performance_timers table.
The threads table contains a row
for each server thread. Each row contains information about a
thread and indicates whether monitoring is enabled for it:
mysql> SELECT * FROM performance_schema.threads\G
*************************** 1. row ***************************
THREAD_ID: 1
NAME: thread/sql/main
TYPE: BACKGROUND
PROCESSLIST_ID: NULL
PROCESSLIST_USER: NULL
PROCESSLIST_HOST: NULL
PROCESSLIST_DB: NULL
PROCESSLIST_COMMAND: NULL
PROCESSLIST_TIME: 80284
PROCESSLIST_STATE: NULL
PROCESSLIST_INFO: NULL
PARENT_THREAD_ID: NULL
ROLE: NULL
INSTRUMENTED: YES
...
*************************** 4. row ***************************
THREAD_ID: 51
NAME: thread/sql/one_connection
TYPE: FOREGROUND
PROCESSLIST_ID: 34
PROCESSLIST_USER: isabella
PROCESSLIST_HOST: localhost
PROCESSLIST_DB: performance_schema
PROCESSLIST_COMMAND: Query
PROCESSLIST_TIME: 0
PROCESSLIST_STATE: Sending data
PROCESSLIST_INFO: SELECT * FROM performance_schema.threads
PARENT_THREAD_ID: 1
ROLE: NULL
INSTRUMENTED: YES
...
When the Performance Schema initializes, it populates the
threads table based on the
threads in existence then. Thereafter, a new row is added each
time the server creates a thread.
The INSTRUMENTED column value for new
threads is determined by the contents of the
setup_actors table. For
information about how to use the
setup_actors table to control
this column, see
Section 22.4.6, “Pre-Filtering by Thread”.
Removal of rows from the threads
table occurs when threads end. For a thread associated with a
client session, removal occurs when the session ends. If a
client has auto-reconnect enabled and the session reconnects
after a disconnect, the session becomes associated with a new
row in the threads table that has
a different PROCESSLIST_ID value. The
initial INSTRUMENTED value for the new
thread may be different from that of the original thread: The
setup_actors table may have
changed in the meantime, and if the
INSTRUMENTED value for the original thread
was changed after it was initialized, that change does not
carry over to the new thread.
The threads table columns with
names having a prefix of PROCESSLIST_
provide information similar to that available from the
INFORMATION_SCHEMA.PROCESSLIST
table or the SHOW PROCESSLIST
statement. Thus, all three sources provide thread-monitoring
information. Use of threads
differs from use of the other two sources in these ways:
Access to threads does not
require a mutex and has minimal impact on server
performance.
INFORMATION_SCHEMA.PROCESSLIST
and SHOW PROCESSLIST have
negative performance consequences because they require a
mutex.
threads provides additional
information for each thread, such as whether it is a
foreground or background thread, and the location within
the server associated with the thread.
threads provides information
about background threads, so it can be used to monitor
activity the other thread information sources cannot.
You can enable or disable thread monitoring (that is,
whether events executed by the thread are instrumented).
To control the initial INSTRUMENTED
value for new foreground threads, use the
setup_actors table. To
control monitoring of existing threads, set the
INSTRUMENTED column of
threads table rows. (For more
information about the conditions under which thread
monitoring occurs, see the description of the
INSTRUMENTED column.)
For these reasons, DBAs who perform server monitoring using
INFORMATION_SCHEMA.PROCESSLIST or
SHOW PROCESSLIST may wish to
monitor using the threads table
instead.
For
INFORMATION_SCHEMA.PROCESSLIST
and SHOW PROCESSLIST,
information about threads for other users is shown only if
the current user has the
PROCESS privilege. That is
not true of the threads table;
all rows are shown to any user who has the
SELECT privilege for the table. Users who
should not be able to see threads for other users should not
be given that privilege.
The threads table has these
columns:
THREAD_ID
A unique thread identifier.
NAME
The name associated with the thread instrumentation code
in the server. For example,
thread/sql/one_connection corresponds
to the thread function in the code responsible for
handling a user connection, and
thread/sql/main stands for the
main() function of the server.
TYPE
The thread type, either FOREGROUND or
BACKGROUND. User connection threads are
foreground threads. Threads associated with internal
server activity are background threads. Examples are
internal InnoDB threads, “binlog
dump” threads sending information to slaves, and
slave I/O and SQL threads.
PROCESSLIST_ID
For threads that are displayed in the
INFORMATION_SCHEMA.PROCESSLIST
table, this is the same value displayed in the
ID column of that table. It is also the
value displayed in the Id column of
SHOW PROCESSLIST output,
and the value that
CONNECTION_ID() would
return within that thread.
For background threads (threads not associated with a user
connection), PROCESSLIST_ID is
NULL, so the values are not unique.
PROCESSLIST_USER
The user associated with a foreground thread,
NULL for a background thread.
PROCESSLIST_HOST
The host name of the client associated with a foreground
thread, NULL for a background thread.
Unlike the HOST column of the
INFORMATION_SCHEMA
PROCESSLIST table or the
Host column of
SHOW PROCESSLIST output,
the PROCESSLIST_HOST column does not
include the port number for TCP/IP connections. To obtain
this information from the Performance Schema, enable the
socket instrumentation (which is not enabled by default)
and examine the
socket_instances table:
mysql>SELECT * FROM performance_schema.setup_instrumentsWHERE NAME LIKE 'wait/io/socket%';+----------------------------------------+---------+-------+ | NAME | ENABLED | TIMED | +----------------------------------------+---------+-------+ | wait/io/socket/sql/server_tcpip_socket | NO | NO | | wait/io/socket/sql/server_unix_socket | NO | NO | | wait/io/socket/sql/client_connection | NO | NO | +----------------------------------------+---------+-------+ 3 rows in set (0.01 sec) mysql>UPDATE performance_schema.setup_instrumentsSET ENABLED='YES'WHERE NAME LIKE 'wait/io/socket%';Query OK, 3 rows affected (0.00 sec) Rows matched: 3 Changed: 3 Warnings: 0 mysql>SELECT * FROM performance_schema.socket_instances\G*************************** 1. row *************************** EVENT_NAME: wait/io/socket/sql/client_connection OBJECT_INSTANCE_BEGIN: 140612577298432 THREAD_ID: 31 SOCKET_ID: 53 IP: ::ffff:127.0.0.1 PORT: 55642 STATE: ACTIVE ...
PROCESSLIST_DB
The default database for the thread, or
NULL if there is none.
PROCESSLIST_COMMAND
For foreground threads, the type of command the thread is
executing on behalf of the client, or
Sleep if the session is idle. For
descriptions of thread commands, see
Section 8.14, “Examining Thread Information”. The value of this
column corresponds to the
COM_
commands of the client/server protocol and
xxxCom_
status variables. See
Section 5.1.9, “Server Status Variables”
xxx
Background threads do not execute commands on behalf of
clients, so this column may be NULL.
PROCESSLIST_TIME
The time in seconds that the thread has been in its current state.
PROCESSLIST_STATE
An action, event, or state that indicates what the thread
is doing. For descriptions of
PROCESSLIST_STATE values, see
Section 8.14, “Examining Thread Information”. If the value if
NULL, the thread may correspond to an
idle client session or the work it is doing is not
instrumented with stages.
Most states correspond to very quick operations. If a thread stays in a given state for many seconds, there might be a problem that bears investigation.
PROCESSLIST_INFO
The statement the thread is executing, or
NULL if it is not executing any
statement. The statement might be the one sent to the
server, or an innermost statement if the statement
executes other statements. For example, if a
CALL statement executes a stored
procedure that is executing a
SELECT statement, the
PROCESSLIST_INFO value shows the
SELECT statement.
PARENT_THREAD_ID
If this thread is a subthread (spawned by another thread),
this is the THREAD_ID value of the
spawning thread. Thread spawning occurs, for example, to
handle insertion of rows from INSERT
DELAYED statements.
ROLE
Unused.
INSTRUMENTED
Whether events executed by the thread are instrumented.
The value is YES or
NO.
For foreground threads, the initial
INSTRUMENTED value is determined by
whether the user account associated with the thread
matches any row in the
setup_actors table.
Matching is based on the values of the
PROCESSLIST_USER and
PROCESSLIST_HOST columns.
If the thread spawns a subthread, matching occurs
again for the threads
table row created for the subthread.
For background threads,
INSTRUMENTED is
YES by default.
setup_actors is not
consulted because there is no associated user for
background threads.
For any thread, its INSTRUMENTED
value can be changed during the lifetime of the
thread. This is the only
threads table column that
can be modified.
For monitoring of events executed by the thread to occur, these things must be true:
The thread_instrumentation consumer
in the setup_consumers
table must be YES.
The threads.INSTRUMENTED column
must be YES.
Monitoring occurs only for those thread events
produced from instruments that have the
ENABLED column set to
YES in the
setup_instruments table.
TRUNCATE TABLE is not permitted
for the threads table.
Table 22.3 Performance Schema Variable Reference
Performance Schema parameters can be specified at server startup on the command line or in option files to configure Performance Schema instruments and consumers. Runtime configuration is also possible in many cases (see Section 22.4, “Performance Schema Runtime Configuration”), but startup configuration must be used when runtime configuration is too late to affect instruments that have already been initialized during the startup process.
Performance Schema consumers and instruments can be configured at startup using the following syntax. For additional details, see Section 22.3, “Performance Schema Startup Configuration”.
--performance-schema-consumer-
consumer_name=value
Configure a Performance Schema consumer. Consumer names in the
setup_consumers table use
underscores, but for consumers set at startup, dashes and
underscores within the name are equivalent. Options for
configuring individual consumers are detailed later in this
section.
--performance-schema-instrument=
instrument_name=value
Configure a Performance Schema instrument. The name may be given as a pattern to configure instruments that match the pattern.
The following items configure individual consumers:
--performance-schema-consumer-events-stages-current=
value
Configure the events-stages-current
consumer.
--performance-schema-consumer-events-stages-history=
value
Configure the events-stages-history
consumer.
--performance-schema-consumer-events-stages-history-long=
value
Configure the events-stages-history-long
consumer.
--performance-schema-consumer-events-statements-current=
value
Configure the events-statements-current
consumer.
--performance-schema-consumer-events-statements-history=
value
Configure the events-statements-history
consumer.
--performance-schema-consumer-events-statements-history-long=
value
Configure the
events-statements-history-long consumer.
--performance-schema-consumer-events-waits-current=
value
Configure the events-waits-current
consumer.
--performance-schema-consumer-events-waits-history=
value
Configure the events-waits-history
consumer.
--performance-schema-consumer-events-waits-history-long=
value
Configure the events-waits-history-long
consumer.
--performance-schema-consumer-global-instrumentation=
value
Configure the global-instrumentation
consumer.
--performance-schema-consumer-statements-digest=
value
Configure the statements-digest consumer.
--performance-schema-consumer-thread-instrumentation=
value
Configure the thread-instrumentation
consumer.
The Performance Schema implements several system variables that provide configuration information:
mysql> SHOW VARIABLES LIKE 'perf%';
+--------------------------------------------------------+---------+
| Variable_name | Value |
+--------------------------------------------------------+---------+
| performance_schema | ON |
| performance_schema_accounts_size | 100 |
| performance_schema_digests_size | 200 |
| performance_schema_events_stages_history_long_size | 10000 |
| performance_schema_events_stages_history_size | 10 |
| performance_schema_events_statements_history_long_size | 10000 |
| performance_schema_events_statements_history_size | 10 |
| performance_schema_events_waits_history_long_size | 10000 |
| performance_schema_events_waits_history_size | 10 |
| performance_schema_hosts_size | 100 |
| performance_schema_max_cond_classes | 80 |
| performance_schema_max_cond_instances | 1000 |
| performance_schema_max_file_classes | 50 |
| performance_schema_max_file_handles | 32768 |
| performance_schema_max_file_instances | 10000 |
| performance_schema_max_mutex_classes | 200 |
| performance_schema_max_mutex_instances | 1000000 |
| performance_schema_max_rwlock_classes | 30 |
| performance_schema_max_rwlock_instances | 1000000 |
| performance_schema_max_socket_classes | 10 |
| performance_schema_max_socket_instances | 1000 |
| performance_schema_max_stage_classes | 150 |
| performance_schema_max_statement_classes | 165 |
| performance_schema_max_table_handles | 10000 |
| performance_schema_max_table_instances | 1000 |
| performance_schema_max_thread_classes | 50 |
| performance_schema_max_thread_instances | 1000 |
| performance_schema_session_connect_attrs_size | 512 |
| performance_schema_setup_actors_size | 100 |
| performance_schema_setup_objects_size | 100 |
| performance_schema_users_size | 100 |
+--------------------------------------------------------+---------+
Performance Schema system variables can be set at server startup on the command line or in option files, and many can be set at runtime. See Section 22.13, “Performance Schema Option and Variable Reference”.
The Performance Schema automatically sizes the values of several of its parameters at server startup if they are not set explicitly. For more information, see Section 22.3, “Performance Schema Startup Configuration”.
Performance Schema system variables have the following meanings:
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema[={OFF|ON}] |
| System Variable | performance_schema |
| Scope | Global |
| Dynamic | No |
| Type | Boolean |
| Default Value | ON |
The value of this variable is ON or
OFF to indicate whether the Performance
Schema is enabled. By default, the value is
ON. At server startup, you can specify this
variable with no value or a value of ON or
1 to enable it, or with a value of OFF or 0
to disable it.
performance_schema_accounts_size
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema-accounts-size=# |
| System Variable | performance_schema_accounts_size |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | -1 (signifies autosizing; do not assign this literal value) |
| Minimum Value | -1 (signifies autosizing; do not assign this literal value) |
| Maximum Value | 1048576 |
The number of rows in the
accounts table. If this variable
is 0, the Performance Schema does not maintain connection
statistics in the accounts table.
performance_schema_digests_size
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema-digests-size=# |
| System Variable | performance_schema_digests_size |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | -1 (signifies autosizing; do not assign this literal value) |
| Minimum Value | -1 |
| Maximum Value | 1048576 |
The maximum number of rows in the
events_statements_summary_by_digest
table. If this maximum is exceeded such that a digest cannot
be instrumented, the Performance Schema increments the
Performance_schema_digest_lost
status variable.
For more information about statement digesting, see Section 22.10, “Performance Schema Statement Digests”.
performance_schema_events_stages_history_long_size
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema-events-stages-history-long-size=# |
| System Variable | performance_schema_events_stages_history_long_size |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | -1 (signifies autosizing; do not assign this literal value) |
The number of rows in the
events_stages_history_long table.
performance_schema_events_stages_history_size
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema-events-stages-history-size=# |
| System Variable | performance_schema_events_stages_history_size |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | -1 (signifies autosizing; do not assign this literal value) |
The number of rows per thread in the
events_stages_history table.
performance_schema_events_statements_history_long_size
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema-events-statements-history-long-size=# |
| System Variable | performance_schema_events_statements_history_long_size |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | -1 (signifies autosizing; do not assign this literal value) |
The number of rows in the
events_statements_history_long
table.
performance_schema_events_statements_history_size
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema-events-statements-history-size=# |
| System Variable | performance_schema_events_statements_history_size |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | -1 (signifies autosizing; do not assign this literal value) |
The number of rows per thread in the
events_statements_history table.
performance_schema_events_waits_history_long_size
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema-events-waits-history-long-size=# |
| System Variable | performance_schema_events_waits_history_long_size |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | -1 (signifies autosizing; do not assign this literal value) |
The number of rows in the
events_waits_history_long table.
performance_schema_events_waits_history_size
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema-events-waits-history-size=# |
| System Variable | performance_schema_events_waits_history_size |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | -1 (signifies autosizing; do not assign this literal value) |
The number of rows per thread in the
events_waits_history table.
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema-hosts-size=# |
| System Variable | performance_schema_hosts_size |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | -1 (signifies autosizing; do not assign this literal value) |
| Minimum Value | -1 (signifies autosizing; do not assign this literal value) |
| Maximum Value | 1048576 |
The number of rows in the hosts
table. If this variable is 0, the Performance Schema does not
maintain connection statistics in the
hosts table.
performance_schema_max_cond_classes
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema-max-cond-classes=# |
| System Variable | performance_schema_max_cond_classes |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | 80 |
| Minimum Value | 0 |
| Maximum Value | 256 |
The maximum number of condition instruments. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.
performance_schema_max_cond_instances
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema-max-cond-instances=# |
| System Variable | performance_schema_max_cond_instances |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | -1 (signifies autosizing; do not assign this literal value) |
The maximum number of instrumented condition objects. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.
performance_schema_max_digest_length
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema-max-digest-length=# |
| Introduced | 5.6.26 |
| System Variable | performance_schema_max_digest_length |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | 1024 |
| Minimum Value | 0 |
| Maximum Value | 1048576 |
The maximum number of bytes of memory reserved per statement
for computation of normalized statement digest values in the
Performance Schema. This variable is related to
max_digest_length; see the
description of that variable in
Section 5.1.7, “Server System Variables”.
For more information about statement digesting, including considerations regarding memory use, see Section 22.10, “Performance Schema Statement Digests”.
performance_schema_max_file_classes
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema-max-file-classes=# |
| System Variable | performance_schema_max_file_classes |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | 50 |
| Minimum Value | 0 |
| Maximum Value | 256 |
The maximum number of file instruments. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.
performance_schema_max_file_handles
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema-max-file-handles=# |
| System Variable | performance_schema_max_file_handles |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | 32768 |
The maximum number of opened file objects. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.
The value of
performance_schema_max_file_handles
should be greater than the value of
open_files_limit:
open_files_limit affects the
maximum number of open file handles the server can support and
performance_schema_max_file_handles
affects how many of these file handles can be instrumented.
performance_schema_max_file_instances
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema-max-file-instances=# |
| System Variable | performance_schema_max_file_instances |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | -1 (signifies autosizing; do not assign this literal value) |
The maximum number of instrumented file objects. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.
performance_schema_max_mutex_classes
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema-max-mutex-classes=# |
| System Variable | performance_schema_max_mutex_classes |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | 200 |
| Minimum Value | 0 |
| Maximum Value | 256 |
The maximum number of mutex instruments. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.
performance_schema_max_mutex_instances
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema-max-mutex-instances=# |
| System Variable | performance_schema_max_mutex_instances |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | -1 (signifies autosizing; do not assign this literal value) |
The maximum number of instrumented mutex objects. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.
performance_schema_max_rwlock_classes
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema-max-rwlock-classes=# |
| System Variable | performance_schema_max_rwlock_classes |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value (>= 5.6.15) | 40 |
| Default Value (<= 5.6.14) | 30 |
| Minimum Value | 0 |
| Maximum Value | 256 |
The maximum number of rwlock instruments. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.
performance_schema_max_rwlock_instances
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema-max-rwlock-instances=# |
| System Variable | performance_schema_max_rwlock_instances |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | -1 (signifies autosizing; do not assign this literal value) |
The maximum number of instrumented rwlock objects. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.
performance_schema_max_socket_classes
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema-max-socket-classes=# |
| System Variable | performance_schema_max_socket_classes |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | 10 |
| Minimum Value | 0 |
| Maximum Value | 256 |
The maximum number of socket instruments. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.
performance_schema_max_socket_instances
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema-max-socket-instances=# |
| System Variable | performance_schema_max_socket_instances |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | -1 (signifies autosizing; do not assign this literal value) |
The maximum number of instrumented socket objects. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.
performance_schema_max_stage_classes
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema-max-stage-classes=# |
| System Variable | performance_schema_max_stage_classes |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | 150 |
| Minimum Value | 0 |
| Maximum Value | 256 |
The maximum number of stage instruments. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.
performance_schema_max_statement_classes
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema-max-statement-classes=# |
| System Variable | performance_schema_max_statement_classes |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | -1 (signifies autosizing; do not assign this literal value) |
The maximum number of statement instruments. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.
The default value is calculated at server build time based on the number of commands in the client/server protocol and the number of SQL statement types supported by the server.
This variable should not be changed, unless to set it to 0 to disable all statement instrumentation and save all memory associated with it. Setting the variable to nonzero values other than the default has no benefit; in particular, values larger than the default cause more memory to be allocated then is needed.
performance_schema_max_table_handles
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema-max-table-handles=# |
| System Variable | performance_schema_max_table_handles |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | -1 (signifies autosizing; do not assign this literal value) |
The maximum number of opened table objects. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.
performance_schema_max_table_instances
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema-max-table-instances=# |
| System Variable | performance_schema_max_table_instances |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | -1 (signifies autosizing; do not assign this literal value) |
The maximum number of instrumented table objects. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.
performance_schema_max_thread_classes
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema-max-thread-classes=# |
| System Variable | performance_schema_max_thread_classes |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | 50 |
| Minimum Value | 0 |
| Maximum Value | 256 |
The maximum number of thread instruments. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.
performance_schema_max_thread_instances
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema-max-thread-instances=# |
| System Variable | performance_schema_max_thread_instances |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | -1 (signifies autosizing; do not assign this literal value) |
The maximum number of instrumented thread objects. The value
controls the size of the threads
table. If this maximum is exceeded such that a thread cannot
be instrumented, the Performance Schema increments the
Performance_schema_thread_instances_lost
status variable. For information about how to set and use this
variable, see
Section 22.7, “Performance Schema Status Monitoring”.
The max_connections system
variable affects how many threads are run in the server.
performance_schema_max_thread_instances
affects how many of these running threads can be instrumented.
The default value of
performance_schema_max_thread_instances
is autosized based on the value of
max_connections.
performance_schema_session_connect_attrs_size
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema-session-connect-attrs-size=# |
| System Variable | performance_schema_session_connect_attrs_size |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | -1 (signifies autosizing; do not assign this literal value) |
| Minimum Value | -1 |
| Maximum Value | 1048576 |
The amount of preallocated memory per thread reserved to hold
connection attribute key-value pairs. If the aggregate size of
connection attribute data sent by a client is larger than this
amount, the Performance Schema truncates the attribute data,
increments the
Performance_schema_session_connect_attrs_lost
status variable, and writes a message to the error log
indicating that truncation occurred if the
log_warnings system variable
value is greater than zero.
The default value of
performance_schema_session_connect_attrs_size
is autosized at server startup. This value may be small, so if
truncation occurs
(Performance_schema_session_connect_attrs_lost
becomes nonzero), you may wish to set
performance_schema_session_connect_attrs_size
explicitly to a larger value.
Although the maximum permitted
performance_schema_session_connect_attrs_size
value is 1MB, the effective maximum is 64KB because the server
imposes a limit of 64KB on the aggregate size of connection
attribute data it will accept. If a client attempts to send
more than 64KB of attribute data, the server rejects the
connection. For more information, see
Section 22.12.8, “Performance Schema Connection Attribute Tables”.
performance_schema_setup_actors_size
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema-setup-actors-size=# |
| System Variable | performance_schema_setup_actors_size |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | 100 |
The number of rows in the
setup_actors table.
performance_schema_setup_objects_size
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema-setup-objects-size=# |
| System Variable | performance_schema_setup_objects_size |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | 100 |
The number of rows in the
setup_objects table.
| Property | Value |
|---|---|
| Command-Line Format | --performance-schema-users-size=# |
| System Variable | performance_schema_users_size |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | -1 (signifies autosizing; do not assign this literal value) |
| Minimum Value | -1 (signifies autosizing; do not assign this literal value) |
| Maximum Value | 1048576 |
The number of rows in the users
table. If this variable is 0, the Performance Schema does not
maintain connection statistics in the
users table.
The Performance Schema implements several status variables that provide information about instrumentation that could not be loaded or created due to memory constraints:
mysql> SHOW STATUS LIKE 'perf%';
+-------------------------------------------+-------+
| Variable_name | Value |
+-------------------------------------------+-------+
| Performance_schema_accounts_lost | 0 |
| Performance_schema_cond_classes_lost | 0 |
| Performance_schema_cond_instances_lost | 0 |
| Performance_schema_file_classes_lost | 0 |
| Performance_schema_file_handles_lost | 0 |
| Performance_schema_file_instances_lost | 0 |
| Performance_schema_hosts_lost | 0 |
| Performance_schema_locker_lost | 0 |
| Performance_schema_mutex_classes_lost | 0 |
| Performance_schema_mutex_instances_lost | 0 |
| Performance_schema_rwlock_classes_lost | 0 |
| Performance_schema_rwlock_instances_lost | 0 |
| Performance_schema_socket_classes_lost | 0 |
| Performance_schema_socket_instances_lost | 0 |
| Performance_schema_stage_classes_lost | 0 |
| Performance_schema_statement_classes_lost | 0 |
| Performance_schema_table_handles_lost | 0 |
| Performance_schema_table_instances_lost | 0 |
| Performance_schema_thread_classes_lost | 0 |
| Performance_schema_thread_instances_lost | 0 |
| Performance_schema_users_lost | 0 |
+-------------------------------------------+-------+
For information on using these variables to check Performance Schema status, see Section 22.7, “Performance Schema Status Monitoring”.
Performance Schema status variables have the following meanings:
Performance_schema_accounts_lost
The number of times a row could not be added to the
accounts table because it was
full.
Performance_schema_cond_classes_lost
How many condition instruments could not be loaded.
Performance_schema_cond_instances_lost
How many condition instrument instances could not be created.
Performance_schema_digest_lost
The number of digest instances that could not be instrumented
in the
events_statements_summary_by_digest
table. This can be nonzero if the value of
performance_schema_digests_size
is too small.
Performance_schema_file_classes_lost
How many file instruments could not be loaded.
Performance_schema_file_handles_lost
How many file instrument instances could not be opened.
Performance_schema_file_instances_lost
How many file instrument instances could not be created.
The number of times a row could not be added to the
hosts table because it was full.
Performance_schema_locker_lost
How many events are “lost” or not recorded, due to the following conditions:
Events are recursive (for example, waiting for A caused a wait on B, which caused a wait on C).
The depth of the nested events stack is greater than the limit imposed by the implementation.
Events recorded by the Performance Schema are not recursive, so this variable should always be 0.
Performance_schema_mutex_classes_lost
How many mutex instruments could not be loaded.
Performance_schema_mutex_instances_lost
How many mutex instrument instances could not be created.
Performance_schema_rwlock_classes_lost
How many rwlock instruments could not be loaded.
Performance_schema_rwlock_instances_lost
How many rwlock instrument instances could not be created.
Performance_schema_session_connect_attrs_lost
The number of connections for which connection attribute
truncation has occurred. For a given connection, if the client
sends connection attribute key-value pairs for which the
aggregate size is larger than the reserved storage permitted
by the value of the
performance_schema_session_connect_attrs_size
system variable, the Performance Schema truncates the
attribute data and increments
Performance_schema_session_connect_attrs_lost.
If this value is nonzero, you may wish to set
performance_schema_session_connect_attrs_size
to a larger value.
For more information about connection attributes, see Section 22.12.8, “Performance Schema Connection Attribute Tables”.
Performance_schema_socket_classes_lost
How many socket instruments could not be loaded.
Performance_schema_socket_instances_lost
How many socket instrument instances could not be created.
Performance_schema_stage_classes_lost
How many stage instruments could not be loaded.
Performance_schema_statement_classes_lost
How many statement instruments could not be loaded.
Performance_schema_table_handles_lost
How many table instrument instances could not be opened.
Performance_schema_table_instances_lost
How many table instrument instances could not be created.
Performance_schema_thread_classes_lost
How many thread instruments could not be loaded.
Performance_schema_thread_instances_lost
The number of thread instances that could not be instrumented
in the threads table. This can be
nonzero if the value of
performance_schema_max_thread_instances
is too small.
The number of times a row could not be added to the
users table because it was full.
Removing a plugin with UNINSTALL
PLUGIN does not affect information already collected for
code in that plugin. Time spent executing the code while the
plugin was loaded was still spent even if the plugin is unloaded
later. The associated event information, including aggregate
information, remains readable in
performance_schema database tables. For
additional information about the effect of plugin installation and
removal, see
Section 22.7, “Performance Schema Status Monitoring”.
A plugin implementor who instruments plugin code should document its instrumentation characteristics to enable those who load the plugin to account for its requirements. For example, a third-party storage engine should include in its documentation how much memory the engine needs for mutex and other instruments.
The Performance Schema is a tool to help a DBA do performance tuning by taking real measurements instead of “wild guesses.” This section demonstrates some ways to use the Performance Schema for this purpose. The discussion here relies on the use of event filtering, which is described in Section 22.4.2, “Performance Schema Event Filtering”.
The following example provides one methodology that you can use to analyze a repeatable problem, such as investigating a performance bottleneck. To begin, you should have a repeatable use case where performance is deemed “too slow” and needs optimization, and you should enable all instrumentation (no pre-filtering at all).
Run the use case.
Using the Performance Schema tables, analyze the root cause of the performance problem. This analysis will rely heavily on post-filtering.
For problem areas that are ruled out, disable the corresponding instruments. For example, if analysis shows that the issue is not related to file I/O in a particular storage engine, disable the file I/O instruments for that engine. Then truncate the history and summary tables to remove previously collected events.
Repeat the process at step 1.
At each iteration, the Performance Schema output, particularly
the events_waits_history_long
table, will contain less and less “noise” caused
by nonsignificant instruments, and given that this table has a
fixed size, will contain more and more data relevant to the
analysis of the problem at hand.
At each iteration, investigation should lead closer and closer to the root cause of the problem, as the “signal/noise” ratio will improve, making analysis easier.
Once a root cause of performance bottleneck is identified, take the appropriate corrective action, such as:
Tune the server parameters (cache sizes, memory, and so forth).
Tune a query by writing it differently,
Tune the database schema (tables, indexes, and so forth).
Tune the code (this applies to storage engine or server developers only).
Start again at step 1, to see the effects of the changes on performance.
The mutex_instances.LOCKED_BY_THREAD_ID and
rwlock_instances.WRITE_LOCKED_BY_THREAD_ID
columns are extremely important for investigating performance
bottlenecks or deadlocks. This is made possible by Performance
Schema instrumentation as follows:
Suppose that thread 1 is stuck waiting for a mutex.
You can determine what the thread is waiting for:
SELECT * FROM performance_schema.events_waits_current
WHERE THREAD_ID = thread_1;
Say the query result identifies that the thread is waiting for
mutex A, found in
events_waits_current.OBJECT_INSTANCE_BEGIN.
You can determine which thread is holding mutex A:
SELECT * FROM performance_schema.mutex_instances
WHERE OBJECT_INSTANCE_BEGIN = mutex_A;
Say the query result identifies that it is thread 2 holding
mutex A, as found in
mutex_instances.LOCKED_BY_THREAD_ID.
You can see what thread 2 is doing:
SELECT * FROM performance_schema.events_waits_current
WHERE THREAD_ID = thread_2;
The following example demonstrates how to use Performance Schema
statement events and stage events to retrieve data comparable to
profiling information provided by SHOW
PROFILES and SHOW
PROFILE statements.
In this example, statement and stage event data is collected in
the events_statements_history_long
and events_stages_history_long
tables. On a busy server with many active foreground threads,
data could age out of the history tables before you are able to
retrieve the information you want to analyze. If you encounter
this problem, options include:
Running the query on a test instance where there is less foreground thread activity.
Disabling instrumentation for other existing foreground
threads by setting the INSTRUMENTED field
of the threads table to
NO for other thread records. For example,
the following statement disables instrumentation for all
foreground threads except the test_user
thread:
mysql>UPDATE performance_schema.threadsSET INSTRUMENTED = 'NO'WHERE TYPE='FOREGROUND' AND PROCESSLIST_USER NOT LIKE 'test_user';
However, be aware that new threads are always instrumented by default.
Increasing the number of rows in the
events_statements_history_long
and events_stages_history_long
tables. The
performance_schema_events_statements_history_size
and
performance_schema_events_stages_history_size
configuration options are autosized by default but can also
be set explicitly at startup. You can view current settings
by running SHOW VARIABLES.
For information about autosized Performance Schema
parameters, see
Section 22.3, “Performance Schema Startup Configuration”.
Performance Schema displays event timer information in
picoseconds (trillionths of a second) to normalize timing data
to a standard unit. In the following example,
TIMER_WAIT values are divided by
1000000000000 to show data in units of seconds. Values are also
truncated to 6 decimal places to display data in the same format
as SHOW PROFILES and
SHOW PROFILE statements.
Ensure that statement and stage instrumentation is enabled
by updating the
setup_instruments table. Some
instruments may already be enabled by default.
mysql>UPDATE performance_schema.setup_instrumentsSET ENABLED = 'YES', TIMED = 'YES'WHERE NAME LIKE '%statement/%';mysql>UPDATE performance_schema.setup_instrumentsSET ENABLED = 'YES', TIMED = 'YES'WHERE NAME LIKE '%stage/%';
Ensure that events_statements_* and
events_stages_* consumers are enabled.
Some consumers may already be enabled by default.
mysql>UPDATE performance_schema.setup_consumersSET ENABLED = 'YES'WHERE NAME LIKE '%events_statements_%';mysql>UPDATE performance_schema.setup_consumersSET ENABLED = 'YES'WHERE NAME LIKE '%events_stages_%';
Run the statement that you want to profile. For example:
mysql> SELECT * FROM employees.employees WHERE emp_no = 10001;
+--------+------------+------------+-----------+--------+------------+
| emp_no | birth_date | first_name | last_name | gender | hire_date |
+--------+------------+------------+-----------+--------+------------+
| 10001 | 1953-09-02 | Georgi | Facello | M | 1986-06-26 |
+--------+------------+------------+-----------+--------+------------+
Identify the EVENT_ID of the statement by
querying the
events_statements_history_long
table. This step is similar to running
SHOW PROFILES to identify the
Query_ID. The following query produces
output similar to SHOW
PROFILES:
mysql> SELECT EVENT_ID, TRUNCATE(TIMER_WAIT/1000000000000,6) as Duration, SQL_TEXT
FROM performance_schema.events_statements_history_long WHERE SQL_TEXT like '%10001%';
+----------+----------+--------------------------------------------------------+
| event_id | duration | sql_text |
+----------+----------+--------------------------------------------------------+
| 31 | 0.028310 | SELECT * FROM employees.employees WHERE emp_no = 10001 |
+----------+----------+--------------------------------------------------------+
Query the
events_stages_history_long
table to retrieve the statement's stage events. Stages are
linked to statements using event nesting. Each stage event
record has a NESTING_EVENT_ID column that
contains the EVENT_ID of the parent
statement.
mysql> SELECT event_name AS Stage, TRUNCATE(TIMER_WAIT/1000000000000,6) AS Duration
FROM performance_schema.events_stages_history_long WHERE NESTING_EVENT_ID=31;
+--------------------------------+----------+
| Stage | Duration |
+--------------------------------+----------+
| stage/sql/starting | 0.000080 |
| stage/sql/checking permissions | 0.000005 |
| stage/sql/Opening tables | 0.027759 |
| stage/sql/init | 0.000052 |
| stage/sql/System lock | 0.000009 |
| stage/sql/optimizing | 0.000006 |
| stage/sql/statistics | 0.000082 |
| stage/sql/preparing | 0.000008 |
| stage/sql/executing | 0.000000 |
| stage/sql/Sending data | 0.000017 |
| stage/sql/end | 0.000001 |
| stage/sql/query end | 0.000004 |
| stage/sql/closing tables | 0.000006 |
| stage/sql/freeing items | 0.000272 |
| stage/sql/cleaning up | 0.000001 |
+--------------------------------+----------+
The Performance Schema avoids using mutexes to collect or produce
data, so there are no guarantees of consistency and results can
sometimes be incorrect. Event values in
performance_schema tables are nondeterministic
and nonrepeatable.
If you save event information in another table, you should not
assume that the original events will still be available later. For
example, if you select events from a
performance_schema table into a temporary
table, intending to join that table with the original table later,
there might be no matches.
mysqldump and BACKUP
DATABASE ignore tables in the
performance_schema database.
Tables in the performance_schema database
cannot be locked with LOCK TABLES, except the
setup_ tables.
xxx
Tables in the performance_schema database
cannot be indexed.
Results for queries that refer to tables in the
performance_schema database are not saved in
the query cache.
Tables in the performance_schema database are
not replicated.
The Performance Schema is not available in
libmysqld, the embedded server.
The types of timers might vary per platform. The
performance_timers table shows which
event timers are available. If the values in this table for a
given timer name are NULL, that timer is not
supported on your platform.
Instruments that apply to storage engines might not be implemented for all storage engines. Instrumentation of each third-party engine is the responsibility of the engine maintainer.