202 DBMS_XPLAN

The DBMS_XPLAN package provides an easy way to display the output of the EXPLAIN PLAN command in several, predefined formats. You can also use the DBMS_XPLAN package to display the plan of a statement stored in the Automatic Workload Repository (AWR) or stored in a SQL tuning set. It further provides a way to display the SQL execution plan and SQL execution runtime statistics for cached SQL cursors based on the information stored in the V$SQL_PLAN and V$SQL_PLAN_STATISTICS_ALL fixed views. Finally, it displays plans from a SQL plan baseline.

See Also:

This chapter contains the following topics:

Using DBMS_XPLAN

Overview

The DBMS_XPLAN package supplies five table functions:

  • DISPLAY - to format and display the contents of a plan table.

  • DISPLAY_AWR - to format and display the contents of the execution plan of a stored SQL statement in the AWR.

  • DISPLAY_CURSOR - to format and display the contents of the execution plan of any loaded cursor.

  • DISPLAY_SQL_PLAN_BASELINE - to display one or more execution plans for the SQL statement identified by SQL handle

  • DISPLAY_SQLSET - to format and display the contents of the execution plan of statements stored in a SQL tuning set.

Security Model

This package runs with the privileges of the calling user, not the package owner (SYS). The table function DISPLAY_CURSOR requires SELECT or READ privileges on the following fixed views: V$SQL_PLAN, V$SESSION and V$SQL_PLAN_STATISTICS_ALL.

Using the DISPLAY_AWR Function requires the user to have SELECT or READ privileges on DBA_HIST_SQL_PLAN, DBA_HIST_SQLTEXT, and V$DATABASE.

Using the DISPLAY_SQLSET Functionrequires the user to have the SELECT or READ privilege on ALL_SQLSET_STATEMENTS and ALL_SQLSET_PLANS.

Using DISPLAY_SQL_PLAN_BASELINE Function requires the user to have the SELECT or READ privilege on DBA_SQL_PLAN_BASELINES as well as the privileges to execute the SQL statement for which the user is trying to get the plan.

All these privileges are automatically granted as part of the SELECT_CATALOG role.

Examples

Displaying a Plan Table Using DBMS_XPLAN.DISPLAY

Execute an explain plan command on a SELECT statement:

EXPLAIN PLAN FOR
SELECT * FROM emp e, dept d
   WHERE e.deptno = d.deptno
   AND e.ename='benoit';

Display the plan using the DBMS_XPLAN.DISPLAY table function

SET LINESIZE 130
SET PAGESIZE 0
SELECT * FROM table(DBMS_XPLAN.DISPLAY);

This query produces the following output:

Plan hash value: 3693697075
---------------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |     1 |    57 |     6  (34)| 00:00:01 |
|*  1 |  HASH JOIN         |      |     1 |    57 |     6  (34)| 00:00:01 |
|*  2 |   TABLE ACCESS FULL| EMP  |     1 |    37 |     3  (34)| 00:00:01 |
|   3 |   TABLE ACCESS FULL| DEPT |     4 |    80 |     3  (34)| 00:00:01 |
---------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------
   1 - access("E"."DEPTNO"="D"."DEPTNO")
   2 - filter("E"."ENAME"='benoit')

15 rows selected.

Displaying a Cursor Execution Plan Using DBMS_XPLAN.DISPLAY_CURSOR

By default, the table function DISPLAY_CURSOR formats the execution plan for the last SQL statement executed by the session. For example:

SELECT ename  FROM  emp e, dept d 
   WHERE   e.deptno = d.deptno  
   AND   e.empno=7369;

ENAME
----------
SMITH

To display the execution plan of the last executed statement for that session:

SET PAGESIZE 0
SELECT * FROM table(DBMS_XPLAN.DISPLAY_CURSOR);

This query produces the following output:

Plan hash value: 3693697075, SQL hash value: 2096952573, child number: 0
------------------------------------------------------------------
SELECT ename FROM emp e, dept d WHERE e.deptno = d.deptno
AND e.empno=7369

---------------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |       |       |            |          |
|*  1 |  HASH JOIN         |      |     1 |    16 |     6  (34)| 00:00:01 |
|*  2 |   TABLE ACCESS FULL| EMP  |     1 |    13 |     3  (34)| 00:00:01 |
|   3 |   TABLE ACCESS FULL| DEPT |     4 |    12 |     3  (34)| 00:00:01 |
---------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------
   1 - access("E"."DEPTNO"="D"."DEPTNO")
   2 - filter("E"."EMPNO"=7369)

21 rows selected.

You can also use the table function DISPLAY_CURSOR to display the execution plan for any loaded cursor stored in the cursor cache. In that case, you must supply a reference to the child cursor to the table function. This includes the SQL ID of the statement and optionally the child number.

Run a query with a distinctive comment:

SELECT /* TOTO */ ename, dname 
FROM dept d join emp e USING (deptno);

Get sql_id and child_number for the preceding statement:

SELECT sql_id, child_number
FROM v$sql 
WHERE sql_text LIKE '%TOTO%';

SQL_ID         CHILD_NUMBER
----------     -----------------------------
gwp663cqh5qbf   0

Display the execution plan for the cursor:

SELECT * FROM table(DBMS_XPLAN.DISPLAY_CURSOR('gwp663cqh5qbf',0));

Plan hash value: 3693697075, SQL ID: gwp663cqh5qbf, child number: 0
--------------------------------------------------------
SELECT /* TOTO */ ename, dname 
FROM dept d JOIN emp e USING (deptno);

----------------------------------------------------------------------------
| Id  | Operation           | Name | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------
|   0 | SELECT STATEMENT    |      |       |       |     7 (100)|          |
|   1 |  SORT GROUP BY      |      |     4 |    64 |     7  (43)| 00:00:01 |
|*  2 |   HASH JOIN         |      |    14 |   224 |     6  (34)| 00:00:01 |
|   3 |    TABLE ACCESS FULL| DEPT |     4 |    44 |     3  (34)| 00:00:01 |
|   4 |    TABLE ACCESS FULL| EMP  |    14 |    70 |     3  (34)| 00:00:01 |
----------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------
   2 - access("E"."DEPTNO"="D"."DEPTNO")

Instead of issuing two queries, one to the get the sql_id and child_number pair and one to display the plan, you can combine these in a single query:

Display the execution plan of all cursors matching the string 'TOTO':

SELECT t.*
FROM v$sql s, table(DBMS_XPLAN.DISPLAY_CURSOR(s.sql_id, s.child_number)) t WHERE sql_text LIKE '%TOTO%';

Displaying a Plan Table with Parallel Information

By default, only relevant information is reported by the display and display_cursor table functions. In Displaying a Plan Table Using DBMS_XPLAN.DISPLAY, the query does not execute in parallel. Hence, information related to the parallelization of the plan is not reported. As shown in the following example, parallel information is reported only if the query executes in parallel.

ALTER TABLE emp PARALLEL;
EXPLAIN PLAN for
SELECT * FROM emp e, dept d
   WHERE e.deptno = d.deptno
   AND e.ename    ='hermann'
   ORDER BY e.empno;

Display the plan using the DBMS_XPLAN.DISPLAY table function

SET LINESIZE 130
SET PAGESIZE 0
SELECT * FROM table(DBMS_XPLAN.DISPLAY);
Plan hash value: 3693697345

-------------------------------------------------------------------------------------------------------------
| Id | Operation          | Name    | Rows | Bytes | Cost (%CPU)| Time     | TQ    |INOUT |PQ Distrib   |
-------------------------------------------------------------------------------------------------------------
| 0  | SELECT STATEMENT   |         | 1    | 117   | 6 (50)     | 00:00:01 |       |      |             |
| 1  | PX COORDINATOR     |         |      |       |            |          |       |      |             |
| 2  | PX SEND QC (ORDER) |:TQ10003 | 1    | 117   | 6 (50)     | 00:00:01 | Q1,03 | P->S | QC (ORDER)  |
| 3  | SORT ORDER BY      |         | 1    | 117   | 6 (50)     | 00:00:01 | Q1,03 | PCWP |             |
| 4  | PX RECEIVE         |         | 1    | 117   | 5 (40)     | 00:00:01 | Q1,03 | PCWP |             |
| 5  | PX SEND RANGE      |:TQ10002 | 1    | 117   | 5 (40)     | 00:00:01 | Q1,02 | P->P | RANGE       |
|* 6 | HASH JOIN          |         | 1    | 117   | 5 (40)     | 00:00:01 | Q1,02 | PCWP |             |
| 7  | PX RECEIVE         |         | 1    | 87    | 2 (50)     | 00:00:01 | Q1,02 | PCWP |             |
| 8  | PX SEND HASH       |:TQ10001 | 1    | 87    | 2 (50)     | 00:00:01 | Q1,01 | P->P | HASH        |
| 9  | PX BLOCK ITERATOR  |         | 1    | 87    | 2 (50)     | 00:00:01 | Q1,01 | PCWC |             |
|* 10| TABLE ACCESS FULL  | EMP     | 1    | 87    | 2 (50)     | 00:00:01 | Q1,01 | PCWP |             |
| 11 | BUFFER SORT        |         |      |       |            |          | Q1,02 | PCWC |             |
| 12 | PX RECEIVE         |         | 4    | 120   | 3 (34)     | 00:00:01 | Q1,02 | PCWP |             |
| 13 | PX SEND HASH       |:TQ10000 | 4    | 120   | 3 (34)     | 00:00:01 |       | S->P | HASH        |
| 14 | TABLE ACCESS FULL  | DEPT    | 4    | 120   | 3 (34)     | 00:00:01 |       |      |             |
-------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
6 - access("E"."DEPTNO"="D"."DEPTNO")
10 - filter("E"."ENAME"='hermann')
---------------------------------------------------

When the query is parallel, information related to parallelism is reported: table queue number (TQ column), table queue type (INOUT) and table queue distribution method (PQ Distrib).

By default, if several plans in the plan table match the statement_id parameter passed to the display table function (default value is NULL), only the plan corresponding to the last EXPLAIN PLAN command is displayed. Hence, there is no need to purge the plan table after each EXPLAIN PLAN. However, you should purge the plan table regularly to ensure good performance in the execution of the DISPLAY table function. If no plan table is created, Oracle uses a global temporary table to store any plan information for individual users and preserves its content throughout the lifespan of a session. Note that you cannot truncate the content of a global temporary table.

For ease of use, you can define a view on top of the display table function and then use that view to display the output of the EXPLAIN PLAN command:

Using a View to Display Last Explain Plan

# define plan view
CREATE VIEW PLAN AS SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY);

# display the output of the last explain plan command
SELECT * FROM PLAN;

Summary of DBMS_XPLAN Subprograms

Table 202-1 DBMS_XPLAN Package Subprograms

Subprogram Description

DIFF_PLAN Function

Compares plans

DISPLAY Function

Displays the contents of the plan table

DISPLAY_AWR Function

Displays the contents of an execution plan stored in the AWR

DISPLAY_CURSOR Function

Displays the execution plan of any cursor in the cursor cache

DISPLAY_PLAN Function

Displays the contents of the plan table in a variety of formats with CLOB output type

DISPLAY_SQL_PLAN_BASELINE Function

Displays one or more execution plans for the specified SQL handle of a SQL plan baseline

DISPLAY_SQLSET Function

Displays the execution plan of a given statement stored in a SQL tuning set

DIFF_PLAN Function

This function compares plans.

Syntax

DBMS_XPLAN.DIFF_PLAN(
   plan1    IN   SPC_SRC,
   plan2    IN   SPC_SRC)
 RETURN VARCHAR2;

Parameters

Table 202-2 DIFF_PLAN Function Parameters

Parameter Description

plan_1

First plan

plan_2

Second plan

DISPLAY Function

This table function displays the contents of the plan table.

In addition, you can use this table function to display any plan (with or without statistics) stored in a table as long as the columns of this table are named the same as columns of the plan table (or V$SQL_PLAN_STATISTICS_ALL if statistics are included). You can apply a predicate on the specified table to select rows of the plan to display.

Syntax

DBMS_XPLAN.DISPLAY(
   table_name    IN  VARCHAR2  DEFAULT 'PLAN_TABLE',
   statement_id  IN  VARCHAR2  DEFAULT  NULL, 
   format        IN  VARCHAR2  DEFAULT  'TYPICAL',
   filter_preds  IN  VARCHAR2 DEFAULT NULL);

Parameters

Table 202-3 DISPLAY Function Parameters

Parameter Description

table_name

Specifies the table name where the plan is stored. This parameter defaults to PLAN_TABLE, which is the default plan table for the EXPLAIN PLAN command. If NULL is specified it also defaults to PLAN_TABLE.

statement_id

Specifies the statement_id of the plan to be displayed. This parameter defaults to NULL, which is the default when the EXPLAIN PLAN command is executed without a set statement_id clause.If no statement_id is specified, the function shows you the plan of the most recent explained statement.

format

Controls the level of details for the plan. It accepts four values:

  • BASIC: Displays the minimum information in the plan—the operation ID, the operation name and its option.

  • TYPICAL: This is the default. Displays the most relevant information in the plan (operation id, name and option, #rows, #bytes and optimizer cost). Pruning, parallel and predicate information are only displayed when applicable. Excludes only PROJECTION, ALIAS and REMOTE SQL information (see below).

  • SERIAL: Like TYPICAL except that the parallel information is not displayed, even if the plan executes in parallel.

  • ALL: Maximum user level. Includes information displayed with the TYPICAL level with additional information (PROJECTION, ALIAS and information about REMOTE SQL if the operation is distributed).

For finer control on the display output, the following keywords can be added to the above three standard format options to customize their default behavior. Each keyword either represents a logical group of plan table columns (such as PARTITION) or logical additions to the base plan table output (such as PREDICATE). Format keywords must be separated by either a comma or a space:

  • ROWS - if relevant, shows the number of rows estimated by the optimizer

  • BYTES - if relevant, shows the number of bytes estimated by the optimizer

  • COST - if relevant, shows optimizer cost information

  • PARTITION - if relevant, shows partition pruning information

  • PARALLEL - if relevant, shows PX information (distribution method and table queue information)

  • PREDICATE - if relevant, shows the predicate section

  • PROJECTION -if relevant, shows the projection section

  • ALIAS - if relevant, shows the "Query Block Name / Object Alias" section

  • REMOTE - if relevant, shows the information for distributed query (for example, remote from serial distribution and remote SQL)

  • NOTE - if relevant, shows the note section of the explain plan

Format keywords can be prefixed by the sign '-' to exclude the specified information. For example, '-PROJECTION' excludes projection information.

If the target plan table (see table_name parameter) also stores plan statistics columns (for example, it is a table used to capture the content of the fixed view V$SQL_PLAN_STATISTICS_ALL), additional format keywords can be used to specify which class of statistics to display when using the DISPLAY Function. These additional format keywords are IOSTATS, MEMSTATS, ALLSTATS and LAST (see the DISPLAY_CURSOR Function or the DISPLAY_SQLSET Function for a full description of these four keywords).

filter_preds

SQL filter predicate(s) to restrict the set of rows selected from the table where the plan is stored. When value is NULL (the default), the plan displayed corresponds to the last executed explain plan. For example: filter_preds=>'plan_id = 10'

Can reference any column of the table where the plan is stored and can contain any SQL construct (for example, sub-query, function calls (see WARNING under Usage Notes)

Usage Notes

Here are some ways you might use variations on the format parameter:

  • Use 'ALL -PROJECTION -NOTE' to display everything except the projection and note sections.

  • Use 'TYPICAL PROJECTION' to display using the typical format with the additional projection section (which is normally excluded under the typical format). Since typical is default, using simply 'PROJECTION' is equivalent.

  • Use '-BYTES -COST -PREDICATE' to display using the typical format but excluding optimizer cost and byte estimates as well as the predicate section.

  • Use 'BASIC ROWS' to display basic information with the additional number of rows estimated by the optimizer.

    WARNING:

    Application developers should expose the filter_preds parameter to end-users only after careful consideration because this could expose the application to SQL injection. Indeed, filter_preds can potentially reference any table or execute any server function for which the database user invoking the table function has privileges.

Examples

To display the result of the last EXPLAIN PLAN command stored in the plan table:

SELECT * FROM table (DBMS_XPLAN.DISPLAY);

To display from other than the default plan table, "my_plan_table":

SELECT * FROM table (DBMS_XPLAN.DISPLAY('my_plan_table'));

To display the minimum plan information:

SELECT * FROM table (DBMS_XPLAN.DISPLAY('plan_table', null, 'basic'));

To display the plan for a statement identified by 'foo', such as statement_id='foo':

SELECT * FROM table (DBMS_XPLAN.DISPLAY('plan_table', 'foo'));

DISPLAY_AWR Function

This table function displays the contents of an execution plan stored in the AWR.

Syntax

DBMS_XPLAN.DISPLAY_AWR( 
   sql_id            IN      VARCHAR2,
   plan_hash_value   IN      NUMBER DEFAULT NULL,
   db_id             IN      NUMBER DEFAULT NULL,
   format            IN      VARCHAR2 DEFAULT TYPICAL);

Parameters

Table 202-4 DISPLAY_AWR Table Function Parameters

Parameter Description

sql_id

Specifies the SQL_ID of the SQL statement. You can retrieve the appropriate value for the SQL statement of interest by querying the column SQL_ID in DBA_HIST_SQLTEXT.

plan_hash_value

Specifies the PLAN_HASH_VALUE of a SQL statement. This parameter is optional. If omitted, the table function returns all stored execution plans for a given SQL_ID.

db_id

Specifies the database_id for which the plan of the SQL statement, identified by SQL_ID should be displayed. If not supplied, the database_id of the local database is used, as shown in V$DATABASE.

format

Controls the level of details for the plan. It accepts four values:

  • BASIC: Displays the minimum information in the plan—the operation ID, the operation name and its option.

  • TYPICAL: This is the default. Displays the most relevant information in the plan (operation id, name and option, #rows, #bytes and optimizer cost). Pruning, parallel and predicate information are only displayed when applicable. Excludes only PROJECTION, ALIAS and REMOTE SQL information (see below).

  • SERIAL: Like TYPICAL except that the parallel information is not displayed, even if the plan executes in parallel.

  • ALL: Maximum user level. Includes information displayed with the TYPICAL level with additional information (PROJECTION, ALIAS and information about REMOTE SQL if the operation is distributed).
 

For finer control on the display output, the following keywords can be added to the above three standard format options to customize their default behavior. Each keyword either represents a logical group of plan table columns (such as PARTITION) or logical additions to the base plan table output (such as PREDICATE). Format keywords must be separated by either a comma or a space:

  • ROWS - if relevant, shows the number of rows estimated by the optimizer

  • BYTES - if relevant, shows the number of bytes estimated by the optimizer

  • COST - if relevant, shows optimizer cost information

  • PARTITION - if relevant, shows partition pruning information

  • PARALLEL - if relevant, shows PX information (distribution method and table queue information)

  • PREDICATE - if relevant, shows the predicate section

  • PROJECTION -if relevant, shows the projection section

  • ALIAS - if relevant, shows the "Query Block Name / Object Alias" section

  • REMOTE - if relevant, shows the information for distributed query (for example, remote from serial distribution and remote SQL)

  • NOTE - if relevant, shows the note section of the explain plan

Format keywords can be prefixed by the sign '-' to exclude the specified information. For example, '-PROJECTION' excludes projection information.

Usage Notes

  • To use the DISPLAY_AWR functionality, the calling user must have SELECT or READ privilege on DBA_HIST_SQL_PLAN, DBA_HIST_SQLTEXT, and V$DATABASE, otherwise it shows an appropriate error message.

  • Here are some ways you might use variations on the format parameter:

    • Use 'ALL -PROJECTION -NOTE' to display everything except the projection and note sections.

    • Use 'TYPICAL PROJECTION' to display using the typical format with the additional projection section (which is normally excluded under the typical format). Since typical is default, using simply 'PROJECTION' is equivalent.

    • Use '-BYTES -COST -PREDICATE' to display using the typical format but excluding optimizer cost and byte estimates as well as the predicate section.

    • Use 'BASIC ROWS' to display basic information with the additional number of rows estimated by the optimizer.

Examples

To display the different execution plans associated with the SQL ID 'atfwcg8anrykp':

SELECT * FROM table(DBMS_XPLAN.DISPLAY_AWR('atfwcg8anrykp'));

To display all execution plans of all stored SQL statements containing the string 'TOTO':

SELECT tf.* FROM DBA_HIST_SQLTEXT ht, table
    (DBMS_XPLAN.DISPLAY_AWR(ht.sql_id,null, null,  'ALL' )) tf 
 WHERE ht.sql_text like '%TOTO%';

DISPLAY_CURSOR Function

This table function displays the explain plan of any cursor loaded in the cursor cache. In addition to the explain plan, various plan statistics (such as. I/O, memory and timing) can be reported (based on the V$SQL_PLAN_STATISTICS_ALL VIEWS).

Syntax

DBMS_XPLAN.DISPLAY_CURSOR(
   sql_id            IN  VARCHAR2  DEFAULT  NULL,
   cursor_child_no   IN  NUMBER    DEFAULT  0, 
   format            IN  VARCHAR2  DEFAULT  'TYPICAL');

Parameters

Table 202-5 DISPLAY_CURSOR Function Parameters

Parameter Description

sql_id

Specifies the SQL_ID of the SQL statement in the cursor cache. You can retrieve the appropriate value by querying the column SQL_ID in V$SQL or V$SQLAREA. Alternatively, you could choose the column PREV_SQL_ID for a specific session out of V$SESSION. This parameter defaults to NULL in which case the plan of the last cursor executed by the session is displayed.

cursor_child_no

Child number of the cursor to display. If not supplied, the execution plan of all cursors matching the supplied sql_id parameter are displayed. The child_number can be specified only if sql_id is specified.

format

Controls the level of details for the plan. It accepts five values:

  • BASIC: Displays the minimum information in the plan—the operation ID, the operation name and its option.

  • TYPICAL: This is the default. Displays the most relevant information in the plan (operation id, name and option, #rows, #bytes and optimizer cost). Pruning, parallel and predicate information are only displayed when applicable. Excludes only PROJECTION, ALIAS and REMOTE SQL information (see below).

  • SERIAL: Like TYPICAL except that the parallel information is not displayed, even if the plan executes in parallel.

  • ALL: Maximum user level. Includes information displayed with the TYPICAL level with additional information (PROJECTION, ALIAS and information about REMOTE SQL if the operation is distributed).

  • ADAPTIVE:

    - Displays the final plan, or the current plan if the execution has not completed. This section includes notes about runtime optimizations that affect the plan, such as switching from a Nested Loops join to a Hash join.

    - Plan lineage. This section shows the plans that were run previously due to automatic reoptimization. It also shows the default plan, if the plan changed due to dynamic plans.

    - Recommended plan. In reporting mode, the plan is chosen based on execution statistics displayed. Note that displaying the recommended plan for automatic reoptimization requires re-compiling the query with the optimizer adjustments collected in the child cursor. Displaying the recommended plan for a dynamic plan does not require this.

    - Dynamic plans. This summarizes the portions of the plan that differ from the default plan chosen by the optimizer.

For finer control on the display output, the following keywords can be added to the above three standard format options to customize their default behavior. Each keyword either represents a logical group of plan table columns (such as PARTITION) or logical additions to the base plan table output (such as PREDICATE).
 

Format keywords must be separated by either a comma or a space:

  • ROWS - if relevant, shows the number of rows estimated by the optimizer

  • BYTES - if relevant, shows the number of bytes estimated by the optimizer

  • COST - if relevant, shows optimizer cost information

  • PARTITION - if relevant, shows partition pruning information

  • PARALLEL - if relevant, shows PX information (distribution method and table queue information)

  • PREDICATE - if relevant, shows the predicate section

  • PROJECTION -if relevant, shows the projection section

  • ALIAS - if relevant, shows the "Query Block Name / Object Alias" section

  • REMOTE - if relevant, shows the information for distributed query (for example, remote from serial distribution and remote SQL)

  • NOTE - if relevant, shows the note section of the explain plan

  • IOSTATS - assuming that basic plan statistics are collected when SQL statements are executed (either by using the gather_plan_statistics hint or by setting the parameter statistics_level to ALL), this format shows IO statistics for ALL (or only for the LAST as shown below) executions of the cursor.

  • MEMSTATS - Assuming that PGA memory management is enabled (that is, pga_aggregate_target parameter is set to a non 0 value), this format allows to display memory management statistics (for example, execution mode of the operator, how much memory was used, number of bytes spilled to disk, and so on). These statistics only apply to memory intensive operations like hash-joins, sort or some bitmap operators.

  • ALLSTATS - A shortcut for 'IOSTATS MEMSTATS'

  • LAST - By default, plan statistics are shown for all executions of the cursor. The keyword LAST can be specified to see only the statistics for the last execution.

The following two formats are deprecated but supported for backward compatibility:

  • RUNSTATS_TOT - Same as IOSTATS, that is, displays IO statistics for all executions of the specified cursor.

  • RUNSTATS_LAST - Same as IOSTATS LAST, that is, displays the runtime statistics for the last execution of the cursor

Format keywords can be prefixed by the sign '-' to exclude the specified information. For example, '-PROJECTION' excludes projection information.

Usage Notes

  • To use the DISPLAY_CURSOR functionality, the calling user must have SELECT or READ privilege on the fixed views V$SQL_PLAN_STATISTICS_ALL, V$SQL and V$SQL_PLAN, otherwise it shows an appropriate error message.

  • Here are some ways you might use variations on the format parameter:

    • Use 'ALL -PROJECTION -NOTE' to display everything except the projection and note sections.

    • Use 'TYPICAL PROJECTION' to display using the typical format with the additional projection section (which is normally excluded under the typical format). Since typical is default, using simply 'PROJECTION' is equivalent.

    • Use '-BYTES -COST -PREDICATE' to display using the typical format but excluding optimizer cost and byte estimates as well as the predicate section.

    • Use 'BASIC ROWS' to display basic information with the additional number of rows estimated by the optimizer.

Examples

To display the execution plan of the last SQL statement executed by the current session:

SELECT * FROM table (
   DBMS_XPLAN.DISPLAY_CURSOR);

To display the execution plan of all children associated with the SQL ID 'atfwcg8anrykp':

SELECT * FROM table (
   DBMS_XPLAN.DISPLAY_CURSOR('atfwcg8anrykp'));

To display runtime statistics for the cursor included in the preceding statement:

SELECT * FROM table (
   DBMS_XPLAN.DISPLAY_CURSOR('atfwcg8anrykp', NULL, 'ALLSTATS LAST');

DISPLAY_PLAN Function

This table function displays the contents of the plan table in a variety of formats with CLOB output type.

Syntax

DBMS_XPLAN.DISPLAY_PLAN (
   table_name       IN    VARCHAR2   DEFAULT 'PLAN_TABLE',
   statement_id     IN    VARCHAR2   DEFAULT NULL,
   format           IN    VARCHAR2   DEFAULT 'TYPICAL',
   filter_preds     IN    VARCHAR2   DEFAULT NULL,
   type             IN    VARCHAR2   DEFAULT 'TEXT')
  RETURN CLOB;

Parameters

Table 202-6 DISPLAY_PLAN Function Parameters

Parameter Description

table_name

Specifies the table name where the plan is stored. This parameter defaults to PLAN_TABLE, which is the default plan table for the EXPLAIN PLAN command. If NULL is specified it also defaults to PLAN_TABLE.

statement_id

Specifies the statement_id of the plan to be displayed. This parameter defaults to NULL, which is the default when the EXPLAIN PLAN command is executed without a set statement_id clause.If no statement_id is specified, the function shows you the plan of the most recent explained statement.

filter_preds

SQL filter predicate(s) to restrict the set of rows selected from the table where the plan is stored. When value is NULL (the default), the plan displayed corresponds to the last executed explain plan. For example: filter_preds=>'plan_id = 10'

Can reference any column of the table where the plan is stored and can contain any SQL construct (for example, sub-query, function calls (see WARNING under Usage Notes)

format

Controls the level of details for the plan. It accepts five values:

  • BASIC: Displays the minimum information in the plan—the operation ID, the operation name and its option.

  • TYPICAL: This is the default. Displays the most relevant information in the plan (operation id, name and option, #rows, #bytes and optimizer cost). Pruning, parallel and predicate information are only displayed when applicable. Excludes only PROJECTION, ALIAS and REMOTE SQL information (see below).

  • SERIAL: Like TYPICAL except that the parallel information is not displayed, even if the plan executes in parallel.

  • ALL: Maximum user level. Includes information displayed with the TYPICAL level with additional information (PROJECTION, ALIAS and information about REMOTE SQL if the operation is distributed).

  • ADAPTIVE: Displays the default plan, and for each dynamic subplan (if stipulated):

    - A list of the rowsources from the original which may be replaced, and the rowsources to replace them

    - If outline display is specified in the format argument, the hints for each option in the dynamic subplan are displayed

For finer control on the display output, the following keywords can be added to the above three standard format options to customize their default behavior. Each keyword either represents a logical group of plan table columns (such as PARTITION) or logical additions to the base plan table output (such as PREDICATE). Format keywords must be separated by either a comma or a space:

  • ROWS - if relevant, shows the number of rows estimated by the optimizer

  • BYTES - if relevant, shows the number of bytes estimated by the optimizer

  • COST - if relevant, shows optimizer cost information

  • PARTITION - if relevant, shows partition pruning information

  • PARALLEL - if relevant, shows PX information (distribution method and table queue information)

  • PREDICATE - if relevant, shows the predicate section

  • PROJECTION -if relevant, shows the projection section

  • ALIAS - if relevant, shows the "Query Block Name / Object Alias" section

  • REMOTE - if relevant, shows the information for distributed query (for example, remote from serial distribution and remote SQL)

  • NOTE - if relevant, shows the note section of the explain plan

Format keywords can be prefixed by the sign '-' to exclude the specified information. For example, '-PROJECTION' excludes projection information.
 

If the target plan table (see table_name parameter) also stores plan statistics columns (for example, it is a table used to capture the content of the fixed view V$SQL_PLAN_STATISTICS_ALL), additional format keywords can be used to specify which class of statistics to display when using the DISPLAY Function. These additional format keywords are IOSTATS, MEMSTATS, ALLSTATS and LAST (see the DISPLAY_CURSOR Function or the DISPLAY_SQLSET Function for a full description of these four keywords).

type

Output type, one of: 'TEXT', 'ACTIVE', 'HTML', or 'XML' (see Usage Notes regarding type ACTIVE). '

Return Values

Returns the requested report as CLOB

Usage Notes

Active reports have a rich, interactive user interface akin to that found in Enterprise Manager while not requiring any EM installation. The report file built is in HTML format, so it can be interpreted by most modern browsers. The code powering the active report is downloaded transparently by the web browser when the report is first viewed, hence viewing it requires outside connectivity.

WARNING:

Application developers should expose the filter_preds parameter to end-users only after careful consideration because this could expose the application to SQL injection. Indeed, filter_preds can potentially reference any table or execute any server function for which the database user invoking the table function has privileges.

DISPLAY_SQL_PLAN_BASELINE Function

This table function displays one or more execution plans for the specified SQL handle of a SQL plan baseline.

Syntax

DBMS_XPLAN.DISPLAY_SQL_PLAN_BASELINE (
   sql_handle      IN VARCHAR2 := NULL,
   plan_name       IN VARCHAR2 := NULL,
   format          IN VARCHAR2 := 'TYPICAL')
 RETURN dbms_xplan_type_table;

Parameters

Table 202-7 DISPLAY_SQL_PLAN_BASELINE Function Parameters

Parameter Description

sql_handle

SQL statement handle. It identifies a SQL statement whose plan(s) are to be displayed.

plan_name

Plan name. It identifies a specific plan. Default NULL means all plans associated with identified SQL statement are explained and displayed.

format

Format string determines what information stored in the plan displayed. One of three format values ('BASIC', 'TYPICAL', 'ALL') can be used, each representing a common use case.

Return Values

A PL/SQL type table

Usage Notes

This procedure uses plan information stored in the plan baseline to explain and display the plans.It is possible that the plan_id stored in the SQL management base may not match with the plan_id of the generated plan. A mismatch between stored plan_id and generated plan_id means that it is a non-reproducible plan. Such a plan is deemed invalid and is bypassed by the optimizer during SQL compilation.

Examples

Display all plans of a SQL statement identified by the SQL handle 'SYS_SQL_b1d49f6074ab95af' using TYPICAL format

SET LINESIZE 150
SET PAGESIZE 2000
SELECT t.*
  FROM TABLE(DBMS_XPLAN.DISPLAY_SQL_PLAN_BASELINE(
                 'SYS_SQL_b1d49f6074ab95af')) t;

Display all plans of one or more SQL statements containing the string 'HR2' using BASIC format

SET LINESIZE 150
SET PAGESIZE 2000
SELECT t.*
   FROM (SELECT DISTINCT sql_handle FROM dba_sql_plan_baselines
         WHERE sql_text like '%HR2%') pb,
        TABLE(DBMS_XPLAN.DISPLAY_SQL_PLAN_BASELINE(pb.sql_handle, NULL,
                                                   'BASIC')) t;

DISPLAY_SQLSET Function

This table function displays the execution plan of a given statement stored in a SQL tuning set.

Syntax

DBMS_XPLAN.DISPLAY_SQLSET(
   sqlset_name      IN  VARCHAR2, 
   sql_id           IN  VARCHAR2,
   plan_hash_value  IN NUMBER := NULL,
   format           IN  VARCHAR2  := 'TYPICAL', 
   sqlset_owner     IN  VARCHAR2  := NULL)
  RETURN DBMS_XPLAN_TYPE_TABLE PIPELINED;

Parameters

Table 202-8 DISPLAY_SQLSET Function Parameters

Parameter Description

sqlset_name

Name of the SQL Tuning Set

sql_id

Specifies the sql_id value for a SQL statement having its plan stored in the SQL tuning set. You can find all stored SQL statements by querying table function DBMS_SQLTUNE.SELECT_SQLSET

plan_hash_value

Optional parameter. Identifies a specific stored execution plan for a SQL statement. If suppressed, all stored execution plans are shown.

format

Controls the level of details for the plan. It accepts four values:

  • BASIC: Displays the minimum information in the plan—the operation ID, the operation name and its option.

  • TYPICAL: This is the default. Displays the most relevant information in the plan (operation id, name and option, #rows, #bytes and optimizer cost). Pruning, parallel and predicate information are only displayed when applicable. Excludes only PROJECTION, ALIAS and REMOTE SQL information (see below).

  • SERIAL: Like TYPICAL except that the parallel information is not displayed, even if the plan executes in parallel.

  • ALL: Maximum user level. Includes information displayed with the TYPICAL level with additional information (PROJECTION, ALIAS and information about REMOTE SQL if the operation is distributed).
 

For finer control on the display output, the following keywords can be added to the above three standard format options to customize their default behavior. Each keyword either represents a logical group of plan table columns (such as PARTITION) or logical additions to the base plan table output (such as PREDICATE). Format keywords must be separated by either a comma or a space:

  • ROWS - if relevant, shows the number of rows estimated by the optimizer

  • BYTES - if relevant, shows the number of bytes estimated by the optimizer

  • COST - if relevant, shows optimizer cost information

  • PARTITION - if relevant, shows partition pruning information

  • PARALLEL - if relevant, shows PX information (distribution method and table queue information)

  • PREDICATE - if relevant, shows the predicate section

  • PROJECTION -if relevant, shows the projection section

  • ALIAS - if relevant, shows the "Query Block Name / Object Alias" section

  • REMOTE - if relevant, shows the information for distributed query (for example, remote from serial distribution and remote SQL)

  • NOTE - if relevant, shows the note section of the explain plan

  • IOSTATS - assuming that basic plan statistics are collected when SQL statements are executed (either by using the gather_plan_statistics hint or by setting the parameter statistics_level to ALL), this format shows IO statistics for ALL (or only for the LAST as shown below) executions of the cursor.

  • MEMSTATS - Assuming that PGA memory management is enabled (that is, pga_aggregate_target parameter is set to a non 0 value), this format allows to display memory management statistics (for example, execution mode of the operator, how much memory was used, number of bytes spilled to disk, and so on). These statistics only apply to memory intensive operations like hash-joins, sort or some bitmap operators.

  • ALLSTATS - A shortcut for 'IOSTATS MEMSTATS'

  • LAST - By default, plan statistics are shown for all executions of the cursor. The keyword LAST can be specified to see only the statistics for the last execution.

The following two formats are deprecated but supported for backward compatibility:

  • RUNSTATS_TOT - Same as IOSTATS, that is, displays IO statistics for all executions of the specified cursor.

  • RUNSTATS_LAST - Same as IOSTATS LAST, that is, displays the runtime statistics for the last execution of the cursor

Format keywords can be prefixed by the sign '-' to exclude the specified information. For example, '-PROJECTION' excludes projection information.

sqlset_owner

The owner of the SQL tuning set. The default is the current user.

Usage Notes

Here are some ways you might use variations on the format parameter:

  • Use 'ALL -PROJECTION -NOTE' to display everything except the projection and note sections.

  • Use 'TYPICAL PROJECTION' to display using the typical format with the additional projection section (which is normally excluded under the typical format). Since typical is default, using simply 'PROJECTION' is equivalent.

  • Use '-BYTES -COST -PREDICATE' to display using the typical format but excluding optimizer cost and byte estimates as well as the predicate section.

  • Use 'BASIC ROWS' to display basic information with the additional number of rows estimated by the optimizer.

Examples

To display the execution plan for the SQL statement associated with SQL ID 'gwp663cqh5qbf' and PLAN HASH 3693697075 in the SQL Tuning Set called 'OLTP_optimization_0405":

SELECT * FROM table (
   DBMS_XPLAN.DISPLAY_SQLSET(
       'OLTP_optimization_0405','gwp663cqh5qbf', 3693697075));

To display all execution plans of the SQL ID 'atfwcg8anrykp' stored in the SQL tuning set:

SELECT * FROM table (
   DBMS_XPLAN.DISPLAY_SQLSET(
      'OLTP_optimization_0405','gwp663cqh5qbf'));

To display runtime statistics for the SQL statement included in the preceding statement:

SELECT * FROM table (
   DBMS_XPLAN.DISPLAY_SQLSET(
      'OLTP_optimization_0405', 'gwp663cqh5qbf', NULL, 'ALLSTATS LAST');