The means by which data is retrieved from a database. For example, a query using an index and a query using a full table scan use different access paths.
The basic properties of a database transaction that all Oracle Database transactions must obey. ACID is an acronym for atomicity, consistency, isolation, and durability.
An online redo log file that may contain data that is required for database instance recovery.
A database session that is using CPU and is not waiting for an event in the idle wait class.
A part of the database self-management framework that samples active database sessions each second, writing the data to memory and persistent storage.
A transaction that has started but not yet committed or rolled back.
A set of capabilities that enables the adaptive optimizer to make run-time adjustments to execution plans and discover additional information that can lead to better optimizer statistics. Adaptive optimization is helpful when existing statistics are not sufficient to generate an optimal plan.
Automatic Database Diagnostic Monitor. An Oracle Database infrastructure that enables a database to diagnose its own performance and determine how identified problems could be resolved.
Automatic Diagnostic Repository. A file-based hierarchical data store for managing information, including network tracing and logging.
The ADR root directory. The ADR base can contain multiple ADR homes, where each ADR home is the root directory for all diagnostic data—traces, dumps, the alert log, and so on—for an instance of an Oracle product or component.
The root directory for all diagnostic data—traces, dumps, the alert log, and so on—for an instance of an Oracle product or component. For example, in an Oracle RAC environment with shared storage and Oracle ASM, each database instance and each Oracle ASM instance has its own ADR home.
An extension of prefix compression that exploits shared intra-column level prefixes, duplicate key elimination, and rowid compression.
A function such as COUNT that operates on a group of rows to return a single row as a result.
A file that provides a chronological log of database messages and errors. The alert log is stored in the ADR.
A "what if" query that answers a business question. Typically, analytic queries involve joins and aggregation, and require scanning a very large amount of input data to produce a relatively small amount of output.
The computing environment in which a database application connects to an Oracle database. The two most common database architectures are client/server and multitier.
An attribute name-value pair in a specified namespace. Applications set various contexts before executing actions on the database.
A feature that enables the replay, in a nondisruptive and rapid manner, of a request against the database after a recoverable error that makes the database session unavailable.
A customized index specific to an application.
Software that provides an interface between the client and one or more database servers, and hosts the applications.
A member of the online redo log that has been archived by Oracle Database. The archived redo log files can be applied to a database backup in media recovery.
A mode of the database that enables the archiving of the online redo log.
An index in which data is stored in ascending order. By default, character data is ordered by the binary values contained in each byte of the value, numeric data from smallest to largest number, and date from earliest to latest value.
A heap-organized table that stores data in close proximity on disk based on user-specified clustering directives.
Automatic Database Diagnostic Monitor (ADDM)
See ADDM.
Automatic Diagnostic Repository (ADR)
See ADR.
The mode in which Oracle Database manages the SGA and instance PGA memory completely automatically.
automatic segment space management (ASSM)
A method of storage space management that uses bitmaps to manage segment space instead of free lists.
automatic undo management mode
A mode of the database in which it automatically manages undo space in a dedicated undo tablespace.
See also manual undo management mode.
Automatic Workload Repository (AWR)
See AWR.
A independent transaction that can be called from another transaction, called the main transaction.
Automatic Workload Repository (AWR). A built-in repository in every Oracle database. Oracle Database periodically makes a snapshot of its vital statistics and workload information and stores them in AWR.
A collection of statistic rates usually taken over a period when the system is performing well at peak load
An index organized like an upside-down tree. A B-tree index has two types of blocks: branch blocks for searching and leaf blocks that store values. The leaf blocks contain every indexed data value and a corresponding rowid used to locate the actual row. The "B" stands for "balanced" because all leaf blocks automatically stay at the same depth.
A process that consolidates functions that would otherwise be handled by multiple Oracle programs running for each client process. The background processes asynchronously perform I/O and monitor other Oracle processes.
See also database instance; Oracle process.
A copy of data. A backup can include crucial parts of the database such as data files, the server parameter file, and control file.
A proprietary RMAN backup format that contains data from one or more data files, archived redo log files, or control files or server parameter file.
An optional, integrated portion of the database buffer cache that uses a temperature-based, object-level replacement algorithm instead of the traditional LRU-based, block-level replacement algorithm.
A placeholder in a SQL statement that must be replaced with a valid value or value address for the statement to execute successfully. By using bind variables, you can write a SQL statement that accepts inputs or parameters at run time. The following example shows a query that uses v_empid as a bind variable:
SELECT * FROM employees WHERE employee_id = :v_empid;
A database index in which the database stores a bitmap for each index key instead of a list of rowids.
A bitmap index for the join of two or more tables.
An operation that merges bitmaps retrieved from bitmap index scans. For example, if the gender and DOB columns have bitmap indexes, then the database may use a bitmap merge if the query predicate is WHERE gender='F' AND DOB > 1966.
A data block that is not in a recognized Oracle format, or whose contents are not internally consistent.
A part of a data block that includes information about the type of block, the address of the block, and sometimes transaction information.
Space in a data block that stores metadata required for managing the block. The overhead includes the block header, table directory, and row directory.
In a B-tree index, a block that the database uses for searching. The leaf blocks store the index entries. The upper-level branch blocks of a B-tree index contain index data that points to lower-level index blocks.
A main memory address in the database buffer cache. A buffer caches currently and recently used data blocks read from disk. When a new block is needed, the database can replace an old data block with a new one.
The measure of how often the database found a requested block in the buffer cache without needing to read it from disk.
The analysis of an organization's information as an aid to making business decisions.
Treatment of strings as a sequence of bytes. Offsets into strings and string lengths are expressed in bytes.
The automatic phase of instance recovery where Oracle Database applies all committed and uncommitted changes in the online redo log files to the affected data blocks.
The ratio of distinct values to the number of table rows. A column with only two distinct values in a million-row table would have low cardinality.
A database administrator who manages a CDB. A PDB administrator manages individual PDBs within the CDB.
A code that pairs each character from a given repertoire with a code unit to facilitate data storage.
Treatment of strings as a sequence of characters. Offsets into strings and string lengths are expressed in characters (character codes).
A constraint on a column or set of columns that requires a specified condition to be true or unknown for every row.
1. A data structure that marks the checkpoint position, which is the SCN in the redo thread where instance recovery must begin. Checkpoints are recorded in the control file and each data file header, and are a crucial element of recovery.
2. The writing of dirty data blocks in the database buffer cache to disk. The database writer (DBW) process writes blocks to disk to synchronize the buffer cache with the data files.
The background process that updates the control file and data file headers with checkpoint information and signals DBW to write blocks to disk.
The cursor containing the plan, compilation environment, and other information for a statement whose text is stored in a parent cursor. The parent cursor is number 0, the first child is number 1, and so on. Child cursors reference exactly the same SQL text as the parent cursor, but are different. For example, two statements with the text SELECT * FROM mytable use different cursors when they reference tables named mytable in different schemas.
A type of control file record that contains noncritical information that is eligible to be overwritten if needed. When all available record slots are full, the database either expands the control file to make room for a new record or overwrites the oldest record.
In client/server architecture, the front-end database application that interacts with a user. The client portion has no data access responsibilities.
The character set for data entered or displayed by a client application. The character set for the client and database can be different.
A process that executes the application or Oracle tool code. When users run client applications such as SQL*Plus, the operating system creates client processes to run the applications.
See also Oracle process.
Software architecture based on a separation of processing between two CPUs, one acting as the client in the transaction, requesting and receiving services, and the other as the server that provides services in a transaction.
A distributed file system that is a cluster of servers that collaborate to provide high performance service to their clients.
A B-tree index on the cluster key.
In a table cluster, the column or columns that the clustered tables have in common. For example, the employees and departments tables share the department_id column. Specify the cluster key when creating the table cluster and when creating every table added to the table cluster.
Vertical space in a table that represents a domain of data. A table definition includes a table name and set of columns. Each column has a name and data type.
The column-based format for objects that reside in the In-Memory Column Store. The columnar format contrasts with the row format that the database uses to store objects in the database buffer cache and in data files.
Action that ends a database transaction and makes permanent all changes performed in the transaction.
The automatic removal of lock-related transaction information (ITL entry) from the blocks after a commit. The database removes the ITL entry only if modified blocks containing data from the committed transaction are still in the SGA, and if no other session is modifying them.
A role that exists in all containers in a multitenant container database (CDB).
In a multitenant container database (CDB), a database user that exists with the same identity in every existing and future PDB.
An execution of the query that defines a materialized view. A complete refresh occurs when you initially create the materialized view, unless the materialized view references a prebuilt table, or you define the table as BUILD DEFERRED.
A partitioning strategy in which a table is partitioned by one data distribution method and then each partition is further divided into subpartitions using a second data distribution method.
A trigger can that can fire at multiple timing points. For example, a compound trigger might fire both before and after the triggering statement.
In Hybrid Columnar Compression, a logical construct that stores a set of rows. When you load data into a table, the database stores groups of rows in columnar format, with the values for each column stored and compressed together. After the database has compressed the column data for a set of rows, the database fits the data into the compression unit.
See composite index.
The combination of one or more expressions and logical operators in a SQL statement that returns a value of TRUE, FALSE, or UNKNOWN. For example, the condition 1=1 always evaluates to TRUE.
In a read committed transaction, an situation that occurs when the transaction attempts to change a row updated by an uncommitted concurrent transaction.
Communication pathway between a client process and an Oracle database instance.
See also session.
A resource utilization and user scalability feature that maximizes the number of sessions over a limited number of protocol connections to a shared server.
A whole database backup that you can open with the RESETLOGS option without performing media recovery. In other words, the backup does not require the application of redo to be made consistent.
See also inconsistent backup.
The retrieval of a read-consistent version of a block in the database buffer cache.
In a multitenant container database (CDB), either the root or a PDB.
In a CDB, a table or view containing data pertaining to multiple containers and possibly the CDB as a whole, along with mechanisms to restrict data visible to specific common users through such objects to one or more containers. Examples of container data objects are Oracle-supplied views whose names begin with V$ and CDB_.
A set of application-defined attributes that validates and secures an application. The SQL statement CREATE CONTEXT creates namespaces for contexts.
A binary file that records the physical structure of a database and contains the names and locations of redo log files, the time stamp of the database creation, the current log sequence number, checkpoint information, and so on.
In a CDB, a DDL statement that affects the CDB itself, multiple containers, multiple common users or roles, or a container other than the one to which the user is connected. Only a common user connected to the root can perform cross-container operations.
An organization of measures with identical dimensions and other shared characteristics. The edges of the cube contain the dimension members, whereas the body of the cube contains the data values.
The online redo log file to which the log writer (LGWR) process is actively writing.
A handle or name for a private SQL area in the PGA. Because cursors are closely associated with private SQL areas, the terms are sometimes used interchangeably.
Simultaneous access of the same data by many users. A multiuser database management system must provide adequate concurrency controls so that data cannot be updated or changed improperly, compromising data integrity.
See also data consistency.
A consistent view of the data by each user in a multiuser database.
See also data concurrency.
An error that occurs when a hardware, software, or network component causes corrupt data to be read or written.
A read-only collection of database tables and views containing reference information about the database, its structures, and its users.
A memory area in the shared pool that holds data dictionary information. The data dictionary cache is also known as the row cache because it holds data as rows instead of buffers, which hold entire data blocks.
A lock that protects the definition of a schema object while an ongoing DDL operation acts on or refers to the object. Oracle Database acquires a DDL lock automatically on behalf of any DDL transaction requiring it. Users cannot explicitly request DDL locks.
A predefined view of tables or other views in the data dictionary. Data dictionary views begin with the prefix DBA_, ALL_, or USER_.
A physical file on disk that was created by Oracle Database and contains the data for a database. The data files can be located either in an operating system file system or Oracle ASM disk group.
Business rules that dictate the standards for acceptable data. These rules are applied to a database by using integrity constraints and triggers to prevent invalid data entry.
The automated search of large stores of data for patterns and trends that transcend simple analysis.
An Oracle Database infrastructure that automatically diagnoses persistent data failures, presents repair options to the user, and executes repairs at the user's request.
The segment containing the data for a nonclustered table, table partition, or table cluster.
See also extent.
In SQL, a fixed set of properties associated with a column value or constant. Examples include VARCHAR2 and NUMBER. Oracle Database treats values of different data types differently.
Restricting data access and database activities. For example, the restriction of users from querying specified tables or executing specified database statements.
A software program that interacts with a database to access and manipulate data.
The process by which a user presents credentials to the database, which verifies the credentials and allows access to the database.
The data block size for a database set when it is created. The size is set for the SYSTEM and SYSAUX tablespaces and is the default for all other tablespaces. The database block size cannot be changed except by re-creating the database.
The portion of the system global area (SGA) that holds copies of data blocks. All client processes concurrently connected to the database instance share access to the buffer cache.
A character encoding scheme that determines which languages can be represented in a database.
The general process of moving data from one or more non-CDBs into a multitenant container database (CDB).
Software that sits between an application and an Oracle database. The driver translates the API calls made by the application into commands that the database can process. By using an ODBC driver, an application can access any data source, including data stored in spreadsheets. The ODBC driver performs all mappings between the ODBC standard and the database.
The combination of the system global area (SGA) and background processes. An instance is associated with one and only one database. In an Oracle Real Application Clusters configuration, multiple instances access a single database simultaneously.
A schema object in one database that enables users to access objects in a different database.
database management system (DBMS)
Software that controls the storage, organization, and retrieval of data.
An object in the database that can be manipulated with SQL. Schema objects such as tables and indexes reside in schemas. Nonschema objects such as directories and roles do not reside in schemas.
In the context of database monitoring, a logical entity that includes a SQL statement, a PL/SQL block, or a composite of the two.
database point-in-time recovery
A type of media recovery that results in a noncurrent version of the database. In this case, you do not apply all of the redo generated after the restored backup.
The aspect of database administration that involves user authentication, encryption, access control, and monitoring.
A server that reliably manages a large amount of data in a multiuser environment so that users can concurrently access the same data. A database server also prevents unauthorized access and provides efficient solutions for failure recovery.
A collection of commodity servers connected together to run on one or more databases.
A collection of low-cost modular storage arrays combined together and accessed by the computers in the Database Server Grid.
A named representation of one or more database instances. The service name for an Oracle database is normally its global database name. Clients use the service name to connect to one or more database instances.
A background process that writes buffers in the database buffer cache to data files.
Data definition language. Includes statements such as CREATE TABLE or ALTER INDEX that define or change a data structure.
A situation in which two or more users are waiting for data locked by each other. Such deadlocks are rare in Oracle Database.
A nonprocedural language that describes what should be done, now how to do it. SQL and Prolog are examples of declarative languages. SQL is declarative in the sense that users specify the result that they want, not how to derive it.
A database configuration in which a server process handles requests for a single client process.
See also shared server.
A constraint that permits a SET CONSTRAINT statement to defer constraint checking until a COMMIT statement is issued. A deferrable constraint enables you to disable the constraint temporarily while making changes that might violate the constraint.
definer's rights PL/SQL procedure
A procedure that executes with the privileges of its owner, not its current user.
The number of parallel execution servers associated with a single operation. Parallel execution is designed to effectively use multiple CPUs. Oracle Database parallel execution framework enables you to either explicitly choose a specific degree of parallelism or to rely on Oracle Database to automatically control it.
In a schema object dependency, the object whose definition references another object. For example, if the definition of object A references object B, then A is a dependent object on B.
An index in which data is stored on a specified column or columns in descending order.
A structure that categorizes data to enable users to answer business questions. Commonly used dimensions are customers, products, and time.
A relational table that stores all or part of the values for a dimension in a star or snowflake schema. Dimension tables typically contain columns for the dimension keys, levels, and attributes.
A database object that specifies an alias for a directory on the server file system where external binary file LOBs (BFILEs) and external table data are located. All directory objects are created in a single namespace and are not owned by an individual schema.
An INSERT in which the database writes data directly to the data files, bypassing the database buffer cache. The database appends the inserted data to the existing data in the table.
Optional background process present only when a shared server configuration is used. Each dispatcher process is responsible for routing requests from connected client processes to available shared server processes and returning the responses.
A set of databases in a distributed system that can appear to applications as a single data source.
The operations that occur when an application distributes its tasks among different computers in a network.
A transaction that includes statements that, individually or as a group, update data on nodes of a distributed database. Oracle Database ensures the integrity of data in distributed transactions using the two-phase commit mechanism.
A lock that prevents destructive interference of simultaneous conflicting DML or DDL operations. DML statements automatically acquire row locks and table locks.
A special views that is continuously updated while a database is open and in use. The dynamic performance views are sometimes called V$ views.
SQL whose complete text is not known until run time. Dynamic SQL statements are stored in character strings that are entered into, or built by, the program at run time.
A private environment in which you can redefine database objects. Edition-based redefinition enables you to upgrade an application's database objects while the application is in use, thus minimizing or eliminating downtime.
The process of transforming data into an unreadable format using a secret key and an encryption algorithm.
Extraction, transformation, and loading (ETL). The process of extracting data from source systems and bringing it into a data warehouse.
A lock that prevents the associated resource from being shared. The first transaction to obtain an exclusive lock on a resource is the only transaction that can alter the resource until the lock is released.
A SQL statement that generates calls to a database instance, including DML and DDL statements and the SET TRANSACTION statement.
The combination of steps used by the database to execute a SQL statement. Each step either retrieves rows of data physically from the database or prepares them for the user issuing the statement. You can override execution plans by using hints.
A combination of one or more values, operators, and SQL functions that evaluates to a value. For example, the expression 2*2 evaluates to 4. In general, expressions assume the data type of their components.
Multiple contiguous data blocks allocated for storing a specific type of information. A segment is made up of one or more extents.
See also data block.
A read-only table whose metadata is stored in the database but whose data in stored in files outside the database. The database uses the metadata describing external tables to expose their data as if they were relational tables.
extraction, transformation, and loading (ETL)
See ETL.
A table in a star schema of a data warehouse that contains factual data. A fact table typically has two types of columns: those that contain facts and those that are foreign keys to dimension tables.
A full index scan in which the database reads all the blocks in the index using multiblock reads, and then discards the branch blocks, returning the index blocks in no particular order.
An optional disk location that stores recovery-related files such as control file and online redo log copies, archived redo log files, flashback logs, and RMAN backups.
The protection provided by a high availability architecture against the failure of a component in the architecture.
A type of database auditing that enables you to audit specific table columns, and to associate event handlers during policy creation.
An internal housekeeping area that contains a variety of information, including general information about the state of the database and the instance, and information communicated between processes.
flashback data archive process (FBDA)
The background process that archives historical rows of tracked tables into Flashback Data Archives. When a transaction containing DML on a tracked table commits, this process stores the pre-image of the changed rows into the Flashback Data Archive. It also keeps metadata on the current rows.
force full database caching mode
The caching mode that is manually enabled by executing the ALTER DATABASE ... FORCE FULL DATABASE CACHING statement. Unlike in the default caching mode, Oracle Database caches the entire database, LOBs specified with the NOCACHE attribute.
An integrity constraint that requires each value in a column or set of columns to match a value in the unique or primary key for a related table. Integrity constraints for foreign keys define actions dictating database behavior if referenced data is altered.
A constraint in which Oracle Database enforces the relationship between two tables that contain one or more common columns. The constraint requires that for each value in the column on which the constraint is defined, the value in the other specified other table and column must match. An example of a referential integrity rule is a rule stating that an employee can only work for an existing department.
A linked list called a free list to manage free space in a segment in manual segment space management (MSSM). For a database object that has free space, a free list keeps track of blocks under the high water mark, which is the dividing line between segment space that is used and not yet used. As blocks are used, the database puts blocks on or removes blocks from the free list as needed.
An index scan in which the database reads only the root and left side branch blocks to find the first leaf block, and then reads the leaf blocks in index sorted order using single block I/O.
A join between two tables that returns the result of an inner join and the result of a left outer join and a right outer join.
A scan of table data in which the database sequentially reads all rows from a table and filters out those that do not meet the selection criteria. The database scans all formatted data blocks under the high water mark (HWM).
A schema object, similar to a PL/SQL procedure, that always returns a single value.
An index that computes the value of a function or expression involving one or more columns and stores it in the index.
A metadata repository, located inside an Oracle database, that is associated with a GDS configuration. Every cloud has one and only one catalog.
A set of databases integrated by the GDS framework into a single virtual server that offers one or more global services while ensuring high performance, availability, and optimal utilization of resources.
See also global service.
A set of databases within a GDS configuration that provides a unique set of global services and belongs to a specific administrative domain.
A logical boundary within a GDS configuration that contains database clients and servers that are geographically close to each other.
An automated workload management solution for replicated databases. Database services are named representations of one or more database instances. GDS implements the Oracle Database service model across a set of replicated databases.
A B-tree index that is partitioned independently of the partitioning scheme used on the indexed table. A single index partition can point to any or all table partitions.
A database service provided by multiple databases synchronized through data replication.
The central management tool in the Global Data Services framework. At least one global service manager must exist in every GDS region of a GDS configuration.
The basic unit of work in parallelism. Oracle Database divides the operation executed in parallel (for example, a table scan, table update, or index creation) into granules. Parallel execution processes execute the operation one granule at a time.
A computing architecture that coordinates large numbers of servers and storage to act as a single large computer.
The software that provides the infrastructure for an enterprise grid architecture. In a cluster, this software includes Oracle Clusterware and Oracle ASM. For a standalone server, this software includes Oracle ASM. Oracle Database combines these products into one software installation called the Grid home.
The steps performed by the database to build a new executable version of application code. The database must perform a hard parse instead of a soft parse if the parsed representation of a submitted statement does not exist in the shared pool.
A type of table cluster that is similar to an indexed cluster, except the index key is replaced with a hash function. No separate cluster index exists. In a hash cluster, the data is the index.
A function that operates on an arbitrary-length input value and returns a fixed-length hash value.
A join in which the database uses the smaller of two tables or data sources to build a hash table in memory. The database scans the larger table, probing the hash table for the addresses of the matching rows in the smaller table.
In a hash cluster, an actual or possible value inserted into the cluster key column. For example, if the cluster key is department_id, then hash key values could be 10, 20, 30, and so on.
A partitioning strategy that maps rows to partitions based on a hashing algorithm that the database applies to the user-specified partitioning key. The destination of a row is determined by the internal hash function applied to the row by the database. The hashing algorithm is designed to distribute rows evenly across devices so that each partition contains about the same number of rows.
An in-memory data structure that associates join keys with rows in a hash join. For example, in a join of the employees and departments tables, the join key might be the department ID. A hash function uses the join key to generate a hash value. This hash value is an index in an array, which is the hash table.
In a hash cluster, a unique numeric ID that identifies a bucket. Oracle Database uses a hash function that accepts an infinite number of hash key values as input and sorts them into a finite number of buckets. Each hash value maps to the database block address for the block that stores the rows corresponding to the hash key value (department 10, 20, 30, and so on).
A mathematical technique in which an infinite set of input values is mapped to a finite set of output values, called hash values. Hashing is useful for rapid lookups of data in a hash table.
A table in which the data rows are stored in no particular order on disk. By default, CREATE TABLE creates a heap-organized table.
A database that organizes data in a tree structure. Each parent record has one or more child records, similar to the structure of a file system.
The boundary between used and unused space in a segment.
An instruction passed to the optimizer through comments in a SQL statement. The optimizer uses hints to choose an execution plan for the statement.
A buffer in the database buffer cache that is frequently accessed and has been recently used.
An outage that occurs when unintentional or malicious actions are committed that cause data in the database to become logically corrupt or unusable.
A bit-for-bit, on-disk duplicate of a data file, control file, or archived redo log file. You can create image copies of physical files with operating system utilities or RMAN and use either tool to restore them.
in-doubt distributed transaction
A distributed transaction in which a two-phase commit is interrupted by any type of system or network failure.
A transaction that is running when an outage breaks the connection between a client application and the database.
A backup in which some files in the backup contain changes made after the checkpoint. Unlike a consistent backup, an inconsistent backup requires media recovery to be made consistent.
incremental-forever backup strategy
The strategy in which an initial level 0 backup is taken to the Recovery Appliance, with all subsequent incremental backups occurring at level 1. The Recovery Appliance creates a virtual full backup by combining the initial level 0 with subsequent level 1 backups.
A refresh that processes only the changes to the existing data in a materialized view. This method eliminates the need for a complete refresh.
Optional schema object associated with a nonclustered table, table partition, or table cluster. In some cases indexes speed data access.
A measure of the row order in relation to an indexed value such as last name. The more order that exists in row storage for this value, the lower the clustering factor.
A table whose storage organization is a variant of a primary B-tree index. Unlike a heap-organized table, data is stored in primary key order.
An ordered scan of an index that has the following characteristics:
The retrieval of a row by traversing an index, using the indexed column values specified by the statement.
An index scan that uses logical subindexes of a composite index. The database "skips" through a single index as if it were searching separate indexes.
An index scan that must have either 0 or 1 rowid associated with an index key. The database performs a unique scan when a predicate references all of the columns in the key of a UNIQUE index using an equality operator.
A configuration parameter such as DB_NAME or SGA_TARGET that affects the operation of a database instance. Settings for initialization parameters are stored in a text-based initialization parameter file or binary server parameter file.
A text file that contains initialization parameter settings for a database instance.
An optional SGA area that stores copies of tables and partitions in a columnar format optimized for rapid scans.
A join of two or more tables that returns only those rows that satisfy the join condition.
The termination of a database instance because of a hardware failure, Oracle internal error, or SHUTDOWN ABORT statement.
The automatic application of redo log records to uncommitted data blocks when an database instance is restarted after a failure.
A trigger that is fired by Oracle Database instead of executing the triggering statement. These triggers are useful for transparently modifying views that cannot be modified directly through DML statements.
See data integrity.
Declarative method of defining a rule for a column. The integrity constraints enforce business rules and prevent the entry of invalid information into tables.
interested transaction list (ITL)
Information in a block header that determines whether a transaction was uncommitted when the database began modifying the block. Entries in the ITL describe which transactions have rows locked and which rows in the block contain committed and uncommitted changes.
An extension of range partitioning that instructs the database to create partitions of the specified range or interval. The database automatically creates the partitions when data inserted into the table exceeds all existing range partitions.
An index that is maintained by DML operations, but is not used by default by the optimizer. Making an index invisible is an alternative to making it unusable or dropping it.
invoker's rights PL/SQL procedure
A procedure that executes in the current user's schema with the current user's privileges.
An area of memory that stores all session-specific Java code and data within the Java Virtual Machine (JVM).
A utility that generates Java classes to represent database entities, such as SQL objects and PL/SQL packages, in a Java client program.
An optional background process that runs user jobs, often in batch mode. A job is a user-defined task scheduled to run one or more times.
A statement that retrieves data from multiple tables specified in the FROM clause. Join types include inner joins, outer joins, and Cartesian joins.
In an attribute-clustered table, clustering that is based on joined columns.
A condition that compares two columns, each from a different table, in a join. The database combines pairs of rows, each containing one row from each table, for which the join condition evaluates to TRUE.
Column or set of columns included in the definition of certain types of integrity constraints.
See prefix compression.
In a join query, a table in which each row appears at most one time in the output of the query.
Alternative name for prefix compression.
See LOB.
Optional area in the SGA that provides large memory allocations for backup and restore operations, I/O server processes, and session memory for the shared server and Oracle XA.
A low-level serialization control mechanism used to protect shared data structures in the SGA from simultaneous access.
The phenomenon that occurs when a process releases the CPU before renewing the latch request.
In a B-tree index, a lower-level block that stores index entries. The upper-level branch blocks of a B-tree index contain index data that points to lower-level index blocks.
The result of a left outer join for table A and B contains all records of the left table A, even if the join condition does not match a record in the right table B. For example, if you perform a left outer join of employees (left) to departments (right), and if some employees are not in a department, then the query returns rows from employees with no matches in departments.
An area of memory in the shared pool. This cache includes the shared SQL areas, private SQL areas (in a shared server configuration), PL/SQL procedures and packages, and control structures such as locks and library cache handles.
In partitioning strategy that uses a list of discrete values as the partition key for each partition. You can use list partitioning to control how individual rows map to specific partitions. By using lists, you can group and organize related sets of data when the key used to identify them is not conveniently ordered.
A process that listens for incoming client connection requests and manages network traffic to the database.
listener registration process (LREG)
The process that registers information about the database instance and dispatcher processes with the Oracle Net listener.
Large object. Large Objects include the following SQL datatypes: BLOB, CLOB, NCLOB, and BFILE. These datatypes are designed for storing data that is large in size.
An index partitioned on the same columns, with the same number of partitions and the same partition bounds as its table. A one-to-one parity exists between index partitions and table partitions.
In a CDB, a role that exists only in a single PDB, just as a role in a non-CDB exists only in the non-CDB. Unlike a common role, a local role may only contain roles and privileges that apply within the container in which the role exists.
In a multitenant container database (CDB), any user that is not a common user.
Within the context of globalization support, a linguistic and cultural environment in which a system or program is running.
A tablespace that uses a bitmap stored in each data file to manage the extents. In contrast, a dictionary-managed tablespace uses the data dictionary to manage space.
A database mechanism that prevents destructive interaction between transactions accessing a shared resource such as a table, row, or system object not visible to users. The main categories of locks are DML locks, DDL locks, and latches and internal locks.
The automatic conversion of a table lock of lower restrictiveness to one of higher restrictiveness. For example, suppose a transaction issues a SELECT ... FOR UPDATE for an employee and later updates the locked row. In this case, the database automatically converts the row share table lock to a row exclusive table lock.
A situation that occurs in some databases when numerous locks are held at one level of granularity (for example, rows) and the database raises the locks to a higher level of granularity (for example, table). Oracle Database never escalates locks.
A number that uniquely identifies a set of redo records in a redo log file. When the database fills one online redo log file and switches to a different one, the database automatically assigns the new file a log sequence number.
The point at which the log writer process (LGWR) stops writing to the active redo log file and switches to the next available redo log file. LGWR switches when either the active redo log file is filled with redo records or a switch is manually initiated.
The background process responsible for redo log buffer management—writing the redo log buffer to the online redo log. LGWR writes all redo entries that have been copied into the buffer since the last time it wrote.
A rowid for an index-organized table. A logical rowid is a base64-encoded representation of a table primary key.
A globally unique identifier that defines a transaction from the application perspective. The logical transaction ID is bound to the database transaction ID.
A software package, available with most operating systems, that enables pieces of multiple physical disks to be combined into a single contiguous address space that appears as one disk to higher layers of software.
A table containing a code column and an associated value column. For example, a job code corresponds to a job name. In contrast to a master table in a pair of master-detail tables, a lookup table is not the means to obtain a detailed result set, such as a list of employees. Rather, a user queries a table such as employees for an employee list and then joins the result set to the lookup table.
A data integrity problem in which one writer of data overwrites the changes of a different writer modifying the same data.
manageability monitor process (MMON)
The background process that performs many tasks related to the Automatic Workload Repository (AWR). For example, MMON writes when a metric violates its threshold value, taking snapshots, and capturing statistics value for recently modified SQL objects.
manual segment space management (MSSM)
A legacy space management method that uses a linked list called a free list to manage free space in a segment.
A mode of the database in which undo blocks are stored in user-managed undo segments. In automatic undo management mode, undo blocks are stored in a system-managed, dedicated undo tablespaces.
In replication, the source of the data that is copied to a subscriber database. The replication agent on the master database reads the records from the transaction log for the master database. It forwards changes to replicated elements to the replication agent on the subscriber database. The replication agent on the subscriber database then applies the updates.
A detail table has a foreign key relationship with a master table. For example, the employees detail table has a foreign key to the departments master table. Unlike a lookup table, a master table is typically queried and then joined to the detail table. For example, a user may query a department in the departments table and then use this result to find the employees in this department.
In a replication environment, a different database with which a materialized view shares data.
In a replication environment, the table associated with a materialized view at a master site.
A schema object that stores the result of a query. Oracle materialized views can be read-only or updatable.
See also view.
The application of redo or incremental backups to a data block or backup data file.
In a PDB, an internal mechanism that points to a dictionary object definition stored in the root. For example, the OBJ$ table in each PDB uses a metadata link to point to the definition of OBJ$ stored in the root.
An database instance that is started and has the database control file open.
The architecture that enables an Oracle database to function as a multitenant container database (CDB), which means that it can contain multiple PDBs. A PDB is a portable collection of schemas, schema objects, and nonschema objects that appears to an Oracle Net client as a traditional Oracle database non-CDB).
multitenant container database (CDB)
See CDB.
multithreaded Oracle Database model
A model that enables Oracle processes to execute as operating system threads in separate address spaces. In threaded mode, some background processes on UNIX and Linux run as processes containing one thread, whereas the remaining Oracle processes run as threads within processes.
An architecture in which one or more application servers provide data for clients and serves as an interface between clients and database servers.
multiversion consistency model
A model that enables the database to present a view of data to multiple concurrent users, with each view consistent to a point in time.
The ability of the database to simultaneously materialize multiple versions of data.
mutual exclusion object (mutex)
A low-level mechanism that prevents an object in memory from aging out or from being corrupted when accessed by concurrent processes.
A meaningful identifier made of existing attributes in a table. For example, a natural key could be a postal code in a lookup table.
A type of database, similar to a hierarchical database, in which records have a many-to-many rather than a one-to-many relationship.
An Oracle database that is not a multitenant container database (CDB). Before Oracle Database 12c, all databases were non-CDBs. Starting in Oracle Database 12c, every database must be either a CDB or a non-CDB.
A control file record that contains critical information that does not change often and cannot be overwritten. Examples of information include tablespaces, data files, online redo log files, and redo threads. Oracle Database never reuses these records unless the corresponding object is dropped from the tablespace.
A constraint whose validity check is never deferred to the end of the transaction. Instead, the database checks the constraint at the end of each statement. If the constraint is violated, then the statement rolls back.
In a PDB, an internal mechanism that points to data (not metadata) in the root. For example, AWR data resides in the root. Each PDB uses an object link to point to the AWR data in the root, thereby making views such as DBA_HIST_ACTIVE_SESS_HISTORY and DBA_HIST_BASELINE accessible in each separate container.
object-relational database management system (ORDBMS)
An RDBMS that implements object-oriented features such as user-defined types, inheritance, and polymorphism.
A schema object that abstracts a real-world entity such as a purchase order. Attributes model the structure of the entity, whereas methods implement operations an application can perform on the entity.
A virtual object table. Each row in the view is an object, which is an instance of a user-defined data type.
Online Analytical Processing. OLAP is characterized by dynamic, dimensional analysis of historical data.
The pool in the UGA that manages OLAP data pages, which are equivalent to data blocks. The page pool is allocated at the start of an OLAP session and released at the end of the session.
Online Transaction Processing. OLTP systems are optimized for fast and reliable transaction handling. Compared to data warehouse systems, most OLTP interactions involve a relatively small number of rows, but a larger group of tables.
The set of two or more online redo log files that record all changes made to Oracle Database data files and control file. When a change is made to the database, Oracle Database generates a redo record in the redo buffer. The log writer process (LGWR) process writes the contents of the redo log buffer to the online redo log.
1. In memory management, operators control the flow of data. Examples include sort, hash join, and bitmap merge operators.
2. In SQL, an operator manipulates data items called operands or arguments and returns a result. Keywords or special characters represent the operators. For example, an asterisk (*) represents the multiplication operator.
Built-in database software that determines the most efficient way to execute a SQL statement by considering factors related to the objects referenced and the conditions specified in the statement.
Details about the database its object used by the optimizer to select the best execution plan for each SQL statement. Categories include table statistics such as numbers of rows, index statistics such as B-tree levels, system statistics such as CPU and I/O performance, and column statistics such as number of nulls.
Memory and process structures used by Oracle Database to manage a database.
A Web application development tool for Oracle Database. Oracle Application Express uses built-in features such as user interface themes, navigational controls, form handlers, and flexible reports to accelerate application development.
Oracle Automatic Storage Management (Oracle ASM)
See Oracle ASM.
Oracle Automatic Storage Management (Oracle ASM). A volume manager and a file system for database files. Oracle ASM is Oracle's recommended storage management solution, providing an alternative to conventional volume managers and file systems.
The fundamental unit of allocation within an ASM disk group. An allocation unit is the smallest contiguous disk space that Oracle ASM allocates. One or more allocation units form an Oracle ASM extent.
A storage device that is provisioned to an Oracle ASM disk group. An Oracle ASM disk can be a physical disk or partition, a Logical Unit Number (LUN) from a storage array, a logical volume, or a network-attached file.
One or more Oracle ASM disks managed as a logical unit. I/O to a disk group is automatically spread across all the disks in the group.
A section of an Oracle ASM file. An Oracle ASM file consists of one or more file extents. Each Oracle ASM extent consists of one or more allocation units on a specific disk.
A file stored in an Oracle ASM disk group. The database can store data files, control files, online redo log files, and other types of files as Oracle ASM files.
A special Oracle instance that manages Oracle ASM disks. Both the Oracle ASM instance and the database instances require shared access to the disks in an Oracle ASM disk group. Oracle ASM instances manage the metadata of the disk group and provide file layout information to the database instances.
A set of components that enables servers to operate together as if they were one server. Oracle Clusterware is a requirement for using Oracle RAC and it is the only clusterware that you need for platforms on which Oracle RAC operates.
A router through which a client connection request may be sent either to its next hop or directly to the database server.
A set of files, located on disk, that store data. Because a database instance and a database are so closely connected, the term Oracle database is often used to refer to both instance and database.
A database security feature that controls when, where, and how databases, data, and applications are accessed.
A feature of Oracle Advanced Security that enables you to mask (redact) data that is queried by low-privileged users or applications.
Oracle Developer Tools for Visual Studio .NET
A set of application tools integrated with the Visual Studio .NET environment. These tools provide GUI access to Oracle functionality, enable the user to perform a wide range of application development tasks, and improve development productivity and ease of use.
A system management tool that provides centralized management of an Oracle database environment.
A group of features that supports viewing past states of data, and winding data back and forth in time, without needing to restore backups.
A large cluster configured using Oracle Clusterware and Oracle Real Application Clusters. These clusters contain two types of nodes arranged in a hub-and-spoke architecture: Hub Nodes and Leaf Nodes.
Oracle Globalization Development Kit (GDK)
A development toolkit that includes comprehensive programming APIs for both Java and PL/SQL, code samples, and documentation that address many of the design, development, and deployment issues encountered while creating global applications.
An integrated development environment (IDE) for building service-oriented applications using the latest industry standards for Java, XML, Web services, and SQL.
A database file naming strategy that enables database administrators to specify operations in terms of database objects rather than file names. Oracle Managed Files eliminates the need for administrators to directly manage the operating system files in a database.
A technology that enables Oracle Database to store, manage, and retrieve images, DICOM format medical images and other objects, audio, video, or other heterogeneous media data in an integrated fashion with other enterprise information.
Communication software that enables a network session between a client application and an Oracle database. After a network session is established, Oracle Net acts as a data courier for the client application and the database.
A process that resides on the server whose responsibility is to listen for incoming client connection requests and manage the traffic to the server. When a client requests a network session with a database, Oracle Net Listener (typically called the listener) receives the request. If the client information matches the listener information, then the listener grants a connection to the database server.
A suite of networking components that provide enterprise-wide connectivity solutions in distributed, heterogeneous computing environments. Oracle Net Services includes Oracle Net, listener, Oracle Connection Manager, Oracle Net Configuration Assistant, and Oracle Net Manager.
A unit of execution that runs the Oracle database code. The process execution architecture depends on the operating system. Oracle processes include server processes and background processes.
Oracle Real Application Clusters. Option that allows multiple concurrent database instances to share a single physical database.
Oracle Real Application Clusters
See Oracle RAC.
A set of advanced features for spatial data and analysis and for physical, logical, network, and social and semantic graph applications. The spatial features provide a schema and functions that facilitate the storage, retrieval, update, and query of collections of spatial features in an Oracle database.
An implementation of the ANSI standard for SQL. Oracle SQL supports numerous features that extend beyond standard SQL.
Oracle Virtual Private Database (VPD)
A security feature that enables you to create security policies to control database access at the row and column level. Essentially, VPD adds a dynamic WHERE clause to a SQL statement that is issued against the table, view, or synonym to which a VPD security policy was applied.
An external interface that allows global transactions to be coordinated by a transaction manager other than Oracle Database.
A set of Oracle Database technologies related to high-performance XML manipulation, storage, and retrieval. Oracle XML DB provides native XML support by encompassing both SQL and XML data models in an interoperable manner.
Oracle XML Developer's Kit (XDK)
A developer toolkit that contains the basic building blocks for reading, manipulating, transforming, and viewing XML documents, whether on a file system or in a database. APIs and tools are available for Java, C, and C++. The production Oracle XDK comes with a commercial redistribution license.
A join that returns all rows that satisfy the join condition and also returns some or all of those rows from one table for which no rows from the other satisfy the join condition.
The application of multiple CPU and I/O resources to the execution of a single database operation.
A lock is held by a SQL statement or PL/SQL program unit for each schema object that it references. Parse locks are acquired so that the associated shared SQL area can be invalidated if a referenced object is altered or dropped.
An index that is correlated with the indexing properties of an associated partitioned table.
A piece of a table or index that shares the same logical attributes as the other partitions. For example, all partitions in a table share the same column and constraint definitions. Each partition is an independent object with its own name and optionally its own storage characteristics.
The exclusion of partitions from a query plan. Whether the optimizer can eliminate partitions from consideration depends on the query predicate. A query that uses a local prefixed index always allows for index partition elimination, whereas a query that uses a local nonprefixed index might not.
A set of one or more columns that determines the partition in which each row in a partitioned table should go. Each row is unambiguously assigned to a single partition.
An index that is divided into smaller and more manageable pieces. Like partitioned tables, partitioned indexes improve manageability, availability, performance, and scalability.
A table that has one or more partitions, each of which is managed individually and can operate independently of the other partitions.
The ability to decompose very large tables and indexes into smaller and more manageable pieces called partitions.
In a multitenant container database (CDB), a portable collection of schemas, schema objects, and nonschema objects that appears to an Oracle Net client as a traditional Oracle database (non-CDB).
A database administrator who manages one or more PDBs. A CDB administrator manages the whole CDB.
PDB/non-CDB compatibility guarantee
In the multitenant architecture, the guarantee that a PDB behaves the same as a non-CDB as seen from a client connecting with Oracle Net.
A tablespace that contains persistent schema objects. Every tablespace that is not a temporary tablespace is a permanent tablespace.
Program global area. A memory buffer that contains data and control information for a server process.
See also SGA.
The physical rowid of an index entry when it was first made. Oracle Database can use physical guesses to probe directly into the leaf block of any index-organized table, bypassing the primary key search.
The part of the optimizer that tries different access paths, join methods, and join orders for a given query block to find the plan with the lowest cost.
Procedural Language/SQL. The Oracle Database procedural language extension to SQL. PL/SQL enables you to mix SQL statements with programmatic constructs such as procedures, functions, and packages.
A PL/SQL block that appears in an application, but is not named or stored in the database. In many applications, PL/SQL blocks may appear wherever SQL statements can appear.
An ordered group of elements, all of the same type. Each element has a unique subscript that determines its position in the collection.
The tool used to define, compile, and run PL/SQL program units. This engine is a special component of many Oracle products, including Oracle Database.
A schema object that consists of a set of SQL statements and other PL/SQL constructs, grouped together, stored in the database, and run as a unit to solve a specific problem or perform a set of related tasks, and that always returns a single value to the caller.
A subset of the server result cache that stores function result sets.
A schema object that consists of a set of SQL statements and other PL/SQL constructs, grouped together, stored in the database, and run as a unit to solve a specific problem or perform a set of related tasks.
A composite variable that can store data values of different types, similar to a struct type in C, C++, or Java. Records are useful for holding data from table rows, or specific columns from table rows.
See PDB.
A directive that instructs the compiler to perform a compilation option. For example, the pragma AUTONOMOUS_TRANSACTION instructs the database that this procedure, when executed, is to be executed as a new autonomous transaction that is independent of its parent transaction.
The total number of digits in a floating-point number. You specify a fixed-point number in the form NUMBER(p,s), where p represents the precision.
A programming tool that enables you to embed SQL statements in a high-level source program written in a language such as C, C++, or COBOL.
The elimination of repeated occurrence of primary key column values in an index-organized table. Prefix compression was formerly known as key compression.
The column or set of columns that uniquely identifies a row in a table. Only one primary key can be defined for each table.
An integrity constraint that disallows duplicate values and nulls in a column or set of columns.
An area in memory that holds a parsed statement and other information for processing. The private SQL area contains data such as bind variable values, query execution state information, and query execution work areas.
The right to run a particular type of SQL statement, or the right to access an object that belongs to another user, run a PL/SQL package, and so on. The types of privileges are defined by Oracle Database.
A security mechanism that captures privilege usage for a database according to a specified condition. For example, you can find the privileges that a user exercised during a specific database session.
A language that describes how things should be done, not what should be done (as in declarative languages). C++ and Java are examples of procedural languages.
A mechanism in an operating system that can run a series of steps. By dividing the work of Oracle Database and database applications into several processes, multiple users and applications can connect to a single database instance simultaneously.
See also background process; Oracle process; client process.
The background process that monitors the other background processes and performs process recovery when a server or dispatcher process terminates abnormally.
See PGA.
A client database whose backups are managed by a Recovery Appliance.
A group of attributes that control how a Recovery Appliance stores and maintains backup data. Each protected database is assigned to exactly one protection policy, which controls all aspects of backup processing for that client.
An operation that retrieves data from tables or views. For example, SELECT * FROM employees is a query.
See also implicit query; subquery.
In parallel execution, the user session or shadow process that coordinates the parallel execution servers. The parallel execution servers performs each operation in parallel if possible. When the parallel servers are finished executing the statement, the query coordinator performs any portion of the work that cannot be executed in parallel. Finally, the query coordinator returns any results to the user.
The execution plan used to execute a query.
An optimization technique that transforms a user request written in terms of master tables into a semantically equivalent request that includes materialized views.
An optimizer component that decides whether it can rewrite the original SQL statement into a semantically equivalent SQL statement with a lower cost.
A type of partitioning in which the database maps rows to partitions based on ranges of values of the partitioning key. Range partitioning is the most common type of partitioning and is often used with dates.
read committed isolation level
An isolation level that guarantees that a query executed by a transaction sees only data committed before the query—not the transaction—began.
A consistent view of data seen by a user. For example, in statement-level read consistency the set of data seen by a SQL statement remains constant throughout statement execution.
See also data concurrency; data consistency.
An isolation level that is similar to the serializable isolation level, with one exception: read-only transactions do not permit data to be modified in the transaction unless the user is SYS.
The continuous transfer of redo changes from the SGA of a protected database to a Recovery Appliance. Real-time redo transport enables RMAN to provide a recovery point objective near 0. Typically, RMAN can recover to within a second of the time when the failure occurred. Protected databases write redo entries directly from the SGA to the Recovery Appliance as they are generated.
A class of errors that arise because of an external system failure, independently of the application session logic that is executing. Recoverable errors occur following planned and unplanned outages of networks, nodes, storage, and databases. An example of a nonrecoverable error is submission of invalid data values.
In a distributed database, the background process that automatically resolves failures in distributed transactions.
Shortened name for Zero Data Loss Recovery Appliance (ZDLRA). Recovery Appliance is an Oracle Engineered System specifically designed to protect Oracle databases. Integrated with RMAN, it enables a centralized, incrementa-forever backup strategy for hundreds to thousands of databases across the enterprise, using cloud-scale, fully fault-tolerant hardware and storage.
Recovery Appliance Backup Module
An Oracle-supplied SBT library that RMAN uses to send backups of protected databases over the network to the Recovery Appliance. The library must be installed in each Oracle home used by a protected database.
The module functions as an SBT media management library that RMAN references when allocating or configuring a channel for backup to the Recovery Appliance. RMAN performs all backups to the Recovery Appliance, and all restores of complete backup sets, using this module.
Recovery Appliance metadata database
The Oracle database that runs inside of the Recovery Appliance. This database stores configuration data such as user definitions, protection policy definitions, and client database definitions. The metadata database also stores backup metadata, including the contents of the delta store.
Recovery Appliance storage location
A set of Oracle ASM disk groups within Recovery Appliance that stores backups. A storage location can be shared among multiple protected databases. Every Recovery Appliance contains the default Recovery Appliance storage location named DELTA.
A centralized backup repository located in an Oracle database. The recovery catalog contains metadata about RMAN backups.
See RMAN.
The time interval within which a protected database must be recoverable to satisfy business requirements. For each protected database in a protection policy, the Recovery Appliance attempts to ensure that the oldest backup on disk is able to support a point-in-time recovery to any time within the specified interval (for example, the past 7 days), counting backward from the current time.
SQL that the database executes in the background to obtain space for database objects. You can think of recursive SQL as "side effect" SQL.
A set of files that protect altered database data in memory that has not been written to the data files. The redo log can consist of two parts: the online redo log and the archived redo log.
Memory structure in the SGA that stores redo entries—a log of changes made to the database. The database writes the redo entries stored in the redo log buffers to an online redo log file, which the database uses when instance recovery is necessary.
A record in the online redo log that holds a group of change vectors, each of which describes a change made to a data block. Each redo log file consists of redo records.
The redo generated by a database instance.
In a foreign key relationship, the primary or unique key to which the foreign key refers. For example, in the common schema, the employees.department_id column is a foreign key, and the departments.department_id column is the referenced key.
In a schema object dependency, the object that is referenced by another object's definition. For example, if the definition of object A references object B, then B is a referenced object for A.
A rule defined on a key in one table that guarantees that the values in that key match the values in a key in a related table (the referenced value).
A database that conforms to the relational model, storing data in a set of simple relations.
relational database management system (RDBMS)
A management system that moves data into a relational database, stores the data, and retrieves it so that applications can manipulate it.
In Application Continuity, opaque information that the database returns to the client driver during normal application run time.
A memory area in the shared pool that Oracle Database can use to allocate large contiguous chunks of memory.
A type of B-tree index that physically reverses the bytes of each index key while keeping the column order. For example, if the index key is 20, and if the two bytes stored for this key in hexadecimal are C1,15 in a standard B-tree index, then a reverse key index stores the bytes as 15,C1.
The result of a right outer join for table A and B contains all records of the right table B, even if the join condition does not match a record in the left table A. For example, if you perform a right outer join of employees (left) to departments (right), and if some departments contain no employees, then the query returns rows from departments with no matches in employees.
Recovery Manager. An Oracle Database utility that backs up, restores, and recovers Oracle databases.
A set of privileges that can be granted to database users or to other roles.
In a multitenant container database (CDB), a collection of schemas, schema objects, and nonschema objects to which all PDBs belong. Every CDB has exactly one root container, which stores the system metadata required to manage PDBs. All PDBs belong to the root.
A set of column information corresponding to a single record in a table. The database stores rows in data blocks.
A situation in which Oracle Database must store a row in a series or chain of blocks because it is too large to fit into a single block.
A lock on a single row of table. A transaction acquires a row lock for each row modified by an INSERT, UPDATE, DELETE, MERGE, or SELECT ... FOR UPDATE statement.
A type of table storage in which all columns of one row are stored together, followed by all columns of the next row, and so on.
A situation in which Oracle Database moves a row from one data block to another data block because the row grows too large to fit in the original block.
A row is stored in a variable-length record. This record is divided into one or more row pieces. Each row piece has a row header and column data.
Software that receives the optimal plan from the optimizer and outputs the execution plan for the SQL statement.
A trigger that fires each time the table is affected by the triggering statement. For example, if a statement updates multiple rows, then a row trigger fires once for each row affected by the UPDATE.
A set of interlinked schemas that enable Oracle documentation and Oracle instructional materials to illustrate common database tasks.
In a floating-point number, the number of digits from the decimal point to the least significant digit. You specify a fixed-point number in the form NUMBER(p,s), where s represents the scale.
A named collection of database objects, including logical structures such as tables and indexes. A schema has the name of the database user who owns it.
A logical structure of data stored in a schema. Examples of schema objects are tables, indexes, sequences, and database links.
System Change Number. A database ordering primitive. The value of an SCN is the logical point in time at which changes are made to a database.
SecureFiles LOB storage is the default storage mechanism for LOBs. The SECUREFILE LOB parameter enables advanced features, including compression and deduplication (part of the Advanced Compression Option) and encryption (part of the Advanced Security Option).
A set of methods for protecting a database from accidental or malicious destruction of data or damage to the database infrastructure.
In a multitenant container database (CDB), a default pluggable database (PDB) that the system uses as a template for user-created PDBs. The name of seed is PDB$SEED.
A set of extents allocated for a specific database object such as a table, index, or table cluster. User segments, undo segments, and temporary segments are all types of segments.
In a SELECT statement, the list of expressions that appears after the SELECT keyword and before the FROM clause.
A value indicating the proportion of a row set retrieved by a predicate or combination of predicates, for example, WHERE last_name = 'Smith'. A selectivity of 0 means that no rows pass the predicate test, whereas a value of 1 means that all rows pass the test.
The adjective selective means roughly "choosy." Thus, a highly selective query returns a low proportion of rows (selectivity close to 0), whereas an unselective query returns a high proportion of rows (selectivity close to 1).
self-referential integrity constraint
A constraint in which a foreign key references a parent key in the same table. For example, a constraint could ensure that every value in the employees.manager_id column corresponds to an existing value in the employees.employee_id column.
A schema object that generates a serial list of unique numbers for table columns.
A single server process performs all necessary processing for the sequential execution of a SQL statement.
A transaction isolation model that enables a transaction to operate in an environment that makes it appear as if no other users were modifying data in the database.
A level of isolation that guarantees that a transaction sees only changes committed at the time the transaction—not the query—began and changes made by the transaction itself.
In a client/server architecture, the computer that runs Oracle software and handles the functions required for concurrent, shared data access. The server receives and processes the SQL and PL/SQL statements that originate from client applications.
A server-side binary file containing initialization parameter settings that is read and written to by the database.
An Oracle process that communicates with a client process and Oracle Database to fulfill user requests. The server processes are associated with a database instance, but are not part of the instance.
A memory pool within the shared pool. This memory pool consists of the SQL query result cache—which stores results of SQL queries—and the PL/SQL function result cache, which stores values returned by PL/SQL functions.
In Oracle Net, a dedicated server process or dispatcher that acts as a connection point to a database.
In Oracle Net, a feature by which the listener registration process (LREG) dynamically registers instance information with a listener, which enables the listener to forward client connection requests to the appropriate service handler.
service-oriented architecture (SOA)
A multitier architecture relying on services that support computer-to-computer interaction over a network.
A logical entity in the database instance memory that represents the state of a current user login to a database. A single connection can have 0, 1, or more sessions established on it.
System global area. A group of shared memory structures that contain data and control information for one Oracle database instance.
A lock that permits the associated resource to be shared by multiple transactions, depending on the operations involved. Multiple transactions can acquire share locks on the same resource.
Portion of the SGA that contains shared memory constructs such as shared SQL areas.
A database configuration that enables multiple client processes to share a small number of server processes.
See also dedicated server.
An area in the shared pool that contains the parse tree and execution plan for a SQL statement. Only one shared SQL area exists for a unique statement.
A trigger on a table that enables you to specify actions for exactly one timing point. For example, the trigger might fire before the firing statement.
A partitioning strategy that uses only one method of data distribution, for example, only list partitioning or only range partitioning.
An event that causes all or a significant portion of an application to stop processing or slow to an unusable service level.
A tablespace that can contain multiple data files or temp files, but the files cannot be as large as in a bigfile tablespace.
The reuse of existing code when the parsed representation of a submitted SQL statement exists in the shared pool and can be shared.
See also hard parse.
A hash cluster that stores the rows corresponding to each value of the hash function in such a way that the database can efficiently return them in sorted order. The database performs the optimized sort internally.
Structured Query Language. A nonprocedural language to access a relational database. Users describe in SQL what they want done, and the SQL language compiler automatically generates a procedure to navigate the database and perform the task. Oracle SQL includes many extensions to the ANSI/ISO standard SQL language.
A graphical version of SQL*Plus, written in Java, that supports development in SQL and PL/SQL.
This stage of SQL processing that involves separating the pieces of a SQL statement into a data structure that can be processed by other routines.
In SQL plan management, a set of one or more accepted plans for a repeatable SQL statement. The effect of a SQL plan baseline is that the optimizer limits its choice to a verified plan in the baseline.
A preventative mechanism that enables the optimizer to automatically manage execution plans, ensuring that the database uses only verified plans.
A set of auxiliary information built during automatic tuning of a SQL statement. A SQL profile is to a SQL statement what statistics are to a table. The optimizer can use SQL profiles to improve cardinality and selectivity estimates, which in turn leads the optimizer to select better plans.
A subset of the server result cache that stores the results of queries and query fragments.
An ANSI standard for embedding SQL statements in Java programs. You can use SQLJ in stored procedures, triggers, and methods within the Oracle Database environment. In addition, you can combine SQLJ programs with JDBC.
Oracle tool used to run SQL statements against Oracle Database.
An independent copy of a production database that you can use for disaster protection in a high availability environment.
A relational schema whose design represents a dimensional data model. The star schema consists of one or more fact tables and one or more dimension tables that are related through foreign keys.
See also dimension table; fact table.
A trigger that is fired once on behalf of the triggering statement, regardless of the number of rows affected by the triggering statement.
The characteristic of a SQL statement as an atomic unit of work that either completely succeeds or completely fails.
statement-level read consistency
The guarantee that data returned by a single query is committed and consistent for a single point in time.
A database operation in which the effects of an unsuccessful SQL statement are rolled back because the statement caused an error during execution.
A named PL/SQL block or Java program that Oracle Database stores in the database. Applications can call stored procedures by name.
A memory pool that stores buffered queue messages and provides memory for Oracle Streams capture processes and apply processes. The Streams pool is used exclusively by Oracle Streams.
Structured Query Language (SQL)
See SQL.
A query nested within another SQL statement. Unlike implicit queries, subqueries use a SELECT statement to retrieve data.
In a data warehouse, an aggregate view that reduces query time by precalculating joins and aggregation operations and storing the results in a table.
A system-generated incrementing identifier that ensures uniqueness within a table. Typically, a sequence generates surrogate keys.
An alias for a schema object. You can use synonyms to provide data independence and location transparency.
See SCN.
An event trigger caused by events such as error messages, or database instance startup and shutdown.
See SGA.
The background process in charge of a variety of system-level cleanup duties, including instance recovery, recovering terminated transactions that were skipped during instance recovery, Cleaning up unused temporary segments, and Coalescing contiguous free extents within dictionary-managed tablespaces.
A schema object that contains data from one or more tables, all of which have one or more columns in common. In table clusters, the database stores together all the rows from all tables that share the same cluster key.
The compression of data segments to reduce disk space in a heap-organized table or table partition.
A user-defined PL/SQL function that returns a collection of rows (a nested table or varray). You can select from this collection as if it were a database table by invoking the table function inside the TABLE clause in a SELECT statement.
A lock on a table that is acquired by a transaction when a table is modified by an INSERT, UPDATE, DELETE, MERGE, SELECT ... FOR UPDATE, or LOCK TABLE statement.
A database storage unit that groups related logical structures together. The database data files are stored in tablespaces.
A file that belongs to a temporary tablespace. The temp files in temporary tablespaces cannot contain permanent database objects.
A segment created by Oracle Database when a SQL statement needs a temporary database area to complete execution.
A table that holds an intermediate result set for the duration of a transaction or a session. Only the current session can see the data in temporary tables.
A tablespace that can only contain transient data that persists only for the duration of a session. No permanent schema objects can reside in a temporary tablespace.
An administrative file that contain diagnostic data used to investigate problems. Oracle Database writes trace files to ADR.
Logical unit of work that contains one or more SQL statements. All statements in a transaction commit or roll back together. The use of transactions is one of the most important ways that a database management system differs from a file system.
Space in the block header that is required for every transaction that updates the block. In data blocks allocated to segments that support transactional changes, free space can also hold transaction entries when the header space is depleted.
A database feature that uses a logical transaction ID to prevent the possibility of a client application submitting duplicate transactions after a recoverable error.
The ability to return a guaranteed outcome for a transaction: whether it committed and whether the call was completed.
An identifier is unique to a transaction and represents the undo segment number, slot, and sequence number.
transaction-level read consistency
The guarantee of read consistency to all queries in a transaction. Each statement in a transaction sees data from the same point in time, which is the time at which the transaction began.
An optional, user-specified tag that serves as a reminder of the work that the transaction is performing. Name a transaction with the SET TRANSACTION ... NAME statement.
A phase of instance recovery in which uncommitted transactions are rolled back.
The data structure within an undo segment that holds the transaction identifiers of the transactions using the undo segment.
The high value of the range partitions determined by the range partition key value.
A database feature that encrypts individual table columns or a tablespace. When a user inserts data into an encrypted column, the database automatically encrypts the data. When users select the column, the data is decrypted. This form of encryption is transparent, provides high performance, and is easy to implement.
A tablespace that you can copy or move between databases. Oracle Data Pump provides the infrastructure for transportable tablespaces.
A PL/SQL or Java procedure that fires when a table or view is modified or when specific user or database actions occur. Procedures are explicitly run, whereas triggers are implicitly run.
A mechanism in a distributed database that guarantees that all databases participating in a distributed transaction either all commit or all undo the statements in the transaction.
User global area. Session memory that stores session variables, such as logon information, and can also contain the OLAP pool.
Records of the actions of transactions, primarily before they are committed. The database can use undo data to logically reverse the effect of SQL statements. Undo data is stored in undo segments.
The minimum amount of time that the database attempts to retain old undo data before overwriting it.
A segment in an undo tablespace.
A tablespace containing undo segments when automatic undo management mode is enabled.
A universal encoded character set that can store information in any language using a single character set.
A policy that you can use to configure auditing on SQL statements, system privileges, schema objects, roles, administrative and non-administrative users, application context values, and policy creations for various applications and events.
An audit trail provides unified storage for audit records from all types of auditing.
An integrity constraint that requires that every value in a column or set of columns be unique.
A data type that can store all types of rowids. Oracle uses universal rowids to store the addresses of index-organized and non-Oracle tables.
An index that is not maintained by DML operations and which the optimizer ignores. All indexes are usable (default) or unusable.
A view that is defined on two or more base tables or views and permits DML operations.
An event trigger that is fired because of events related to user logon and logoff, DDL statements, and DML statements.
See UGA.
The name by which a user is known to Oracle Database and to other users. Every user name is associated with a password, and both must be entered to connect to Oracle Database.
See client process.
A named set of resource limits and password parameters that restrict database usage and database instance resources for a user.
A custom-tailored presentation of the data in one or more tables. The views do not actually contain or store data, but derive it from the tables on which they are based.
A column that is not stored on disk. The database derives the values in virtual columns on demand by computing a set of expressions or functions.
A complete database image as of one distinct point in time, maintained efficiently by a Recovery Appliance through the indexing of incremental backups from a protected database. The virtual full backups contain individual blocks from multiple incremental backups. For example, if you take a level 0 backup on Monday with SCN 10000, and if you take an incremental level 1 backup on Tuesday with SCN 11000, then the Recovery Appliance metadata database shows a virtual level 0 backup current to SCN 11000.
A backup of the control file and all data files that belong to a database.
The protocol that mandates that before the database writer process can write a dirty buffer, the database must write to disk the redo records associated with changes to the buffer.
Within a zone map, a zone is a set of contiguous data blocks that stores the minimum and maximum values of relevant columns.
Within an attribute-clustered table, a zone map is an independent access structure that divides data blocks into zones.