Glossary Oracle 12.2
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.active transaction
A transaction that has started but not yet committed or rolled back.access driver
In the external table infrastructure, the API that interprets the external data for the database. The access driver runs inside the database, which uses the driver to read the data in the external table.access path
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.ACID properties
The basic properties of a database transaction that all Oracle Database transactions must obey. ACID is an acronym for atomicity, consistency, isolation, and durability.active online redo log file
An online redo log file that may contain data that is required for database instance recovery.active session
A database session that is using CPU and is not waiting for an event in the idle wait class.Active Session History (ASH)
A part of the database self-management framework that samples active database sessions each second, writing the data to memory and persistent storage.active transaction
A transaction that has started but not yet committed or rolled back.adaptive query optimization
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.ADDM
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.ADR
Automatic Diagnostic Repository. A file-based hierarchical data store for managing information, including network tracing and logging.ADR base
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.ADR home
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.advanced index compression
An extension and enhancement of prefix compression for supported unique and non-unique indexes on heap-organized tables. Unlike prefix compression, which uses fixed duplicate key elimination for every block, advanced compression uses adaptive duplicate key elimination on a per-block basis.advanced row compression
A type of table compression, intended for OLTP applications, that compresses data manipulated by any SQL operation.
See also basic table compression.aggregate function
A function such as COUNT that operates on a group of rows to return a single row as a result.alert log
A file that provides a chronological log of database messages and errors. The alert log is stored in the ADR.analytic function
A function that operates on a group of rows to return multiple rows as a result.analytic query
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.antijoin
Within an application root, an application is a named, versioned set of data and metadata created by a common user. To install an application, execute ALTER PDB APPLICATION BEGIN INSTALL, then execute user-created SQL statements, and then end by executing ALTER PDB APPLICATION BEGIN INSTALL. An application might include a application common user, an application common object, or some multiple and combination of the preceding.
The computing environment in which a database application connects to an Oracle database. The two most common database architectures are client/server and multitier.
application common object
application common user
application containerapplication server
A named set of application PDBs plugged in to an application root. An application container may contain an application seed.
An attribute name-value pair in a specified namespace. Applications set various contexts before executing actions on the database.Application Continuity
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.application domain index
A customized index specific to an application.
The root container within an application container. Every application container has exactly one application root. An application root shares some characteristics with the CDB root, because it can contain common objects, and some characteristics with a PDB, because it is created with the CREATE PLUGGABLE DATABASE statement.
Software that provides an interface between the client and one or more database servers, and hosts the applications.
Hybrid Columnar Compression specified with COLUMN STORE COMPRESS FOR ARCHIVE. This type uses higher compression ratios than COLUMN STORE COMPRESS FOR QUERY, and is useful for compressing data that will be stored for long periods of time.
archived redo log file
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.archiver process (ARCn)
The background process that archives online redo log files.archiving
The operation of generating an archived redo log file.ascending index
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.attribute-clustered table
A heap-organized table that stores data in close proximity on disk based on user-specified clustering directives.audit trail
A location that stores audit records.Automatic Database Diagnostic Monitor (ADDM)
See ADDM.Automatic Diagnostic Repository (ADR)
See ADR.automatic memory management
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.autonomous transaction
A independent transaction that can be called from another transaction, called the main transaction.AWR
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.b>AWR baseline
A collection of statistic rates usually taken over a period when the system is performing well at peak loadAWR snapshot
A set of performance statistics captured in AWR at a specific time.B-tree index
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.background process
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.backup
A copy of data. A backup can include crucial parts of the database such as data files, the server parameter file, and control file.backup piece
The smallest unit of a backup set.backup set
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.basic table compression
A type of table compression intended for bulk load operations. You must use direct path INSERT operations, ALTER TABLE . . . MOVE operations, or online table redefinition to achieve basic table compression.
big table cache
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.bigfile tablespace
A tablespace that contains one very large data file or temp file.bind variable
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;bitmap index
A database index in which the database stores a bitmap for each index key instead of a list of rowids.bitmap join index
A bitmap index for the join of two or more tables.bitmap merge
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.block corruption
A data block that is not in a recognized Oracle format, or whose contents are not internally consistent.block header block overhead branch block
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.buffer
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.buffer header
A memory structure that stores metadata about a buffer.buffer cache hit ratio
The measure of how often the database found a requested block in the buffer cache without needing to read it from disk.buffer pool
A collection of buffers in the SGA.business intelligence
The analysis of an organization's information as an aid to making business decisions.byte semantics
Treatment of strings as a sequence of bytes. Offsets into strings and string lengths are expressed in bytes.cache recovery cardinality
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.Cartesian join
A join in which one or more of the tables does not have any join conditions to any other tables in the statement. The optimizer joins every row from one data source with every row from the other data source, creating the Cartesian product of the two sets.CDB CDB administrator
A database administrator who manages a CDB. A PDB administrator manages individual PDBs within the CDB.CDB restore point
In a CDB, a restore point that is created when connected to the root, and when the FOR PLUGGABLE DATABASE clause is not specified. Unlike a PDB restore point, a CDB restore point is usable by all PDBs.
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 CDB root.character encoding
A code that pairs each character from a given repertoire with a code unit to facilitate data storage.character semantics
Treatment of strings as a sequence of characters. Offsets into strings and string lengths are expressed in characters (character codes).character set
An encoding scheme used to display characters on your computer screen.check constraint
A constraint on a column or set of columns that requires a specified condition to be true or unknown for every row.checkpoint
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.checkpoint process (CKPT)
The background process that updates the control file and data file headers with checkpoint information and signals DBW to write blocks to disk.child cursor
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.circular reuse record
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.clean restore point
A PDB restore point that is created when the PDB is closed. A Flashback PDB to a clean restore point does not require restoring backups or creating a temporary instance.
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.
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.
An object that resides either in the CDB root or an application root that shares either data (a data-linked common object) or metadata (a metadata-linked common object). All common objects in the CDB root are Oracle-supplied. A common object in an application root is called an application common object.
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 multiple containers. A common user created in the CDB root has the same identity in every existing and future PDB. A common user created in an application container has the same identity in every existing and future application PDB in this application container.
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.
Activity between two points in time in a single database session.
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 set of two or more columns with a unique key constraint.
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, a situation that occurs when the transaction attempts to change a row updated by an uncommitted concurrent transaction.
A resource utilization and user scalability feature that maximizes the number of sessions over a limited number of protocol connections to a shared server.
The retrieval of a version of a block in the database buffer cache that is consistent to a specific SCN (part of read consistency). If the database needs a block to satisfy a query, and if no block in the database buffer cache is consistent to the correct SCN, then the database attempts to obtain the correct version of the block from undo data.
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.
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 retrieval of the version of a data block as it exists right now in the buffer cache, without using read consistency. Only one version of a block exists in current mode at any one time.
The online redo log file to which the log writer (LGWR) process is actively writing.
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.
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.
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.
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.
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. Every database instance is either a read/write database instance or a read-only database instance. In an Oracle Real Application Clusters configuration, multiple instances access a single database.
A schema object in one database that enables users to access objects in a different database.
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.
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.
An account through which you can log in to an Oracle database.
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.
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.
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.
A single or multiblock read into the PGA, bypassing the SGA.
The situation that occurs when a transaction reads uncommitted data written by another transaction. Oracle Database never permits dirty reads.
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.
A network of disparate systems that seamlessly communicate with each other.
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.
Data manipulation language. Includes statements such as SELECT, INSERT, UPDATE, and DELETE.
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.
A join with a join condition containing an equality operator.
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 a hint.
A combination of one or more values, operators, and SQL functions that resolves to a value. For example, the expression 2*2 evaluates to 4. In general, expressions assume the data type of their components.
A hybrid of a data-linked common object and a metadata-linked common object. For an extended data-linked object, each application PDB can create its own PDB-specific data while sharing the common data in the application root.
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.
Data that represents a business measure, such as sales or cost data.
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.
In a table, the intersection of a row and column.
A data structure built inside a contiguous disk address space.
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.
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.
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. For example, a referential integrity rule might state that an employee can only work for an existing department.
A character literal that describes the format of a datetime in a character string.
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 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.
The combination of the database name (DB_NAME) and network domain (DB_DOMAIN), for example, orcl.example.com. The global database domain is unique within a network.
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 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.
Hashing multiple input values to the same output value.
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.
A buffer in the database buffer cache that is frequently accessed and has been recently used.
Cloning a PDB while the source PDB is open in read/write mode.
An outage that occurs when unintentional or malicious actions are committed that cause data in the database to become logically corrupt or unusable.
A hybrid method that uses row and columnar techniques to compress data in a data block. A logical construct called a compression unit is used to store a set of hybrid columnar-compressed rows.
An optional SGA area that stores copies of tables and partitions in a columnar format optimized for rapid scans.
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.
A component of a DML statement that retrieves data without a subquery. An UPDATE, DELETE, or MERGE statement that does not explicitly include a SELECT statement uses an implicit query to retrieve the rows to be modified.
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.
See IM column store.
An online redo log file that is not required for instance recovery.
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 special type of data block that manages space differently from table blocks.
An table cluster that uses an index to locate data. The cluster index is a B-tree index on the cluster key.
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.
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 formal system for storing and processing information.
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 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 collection of individual PGAs in a database instance.
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.
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.
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 Java method published to SQL and stored in the database.
A language-independent, text-based data format that can represent objects, arrays, and scalar data.
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.
A view whose definition includes multiple tables or views in the FROM clause.
A virtual processor that runs compiled Java code.
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.
Individual values in a key.
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.
The phenomenon that occurs when a process repeatedly requests a latch in a loop.
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.
A 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.
The process that registers information about the database instance and dispatcher processes with the Oracle Net listener.
A fixed data value.
Large object. Large Objects include the following SQL data types: BLOB, CLOB, NCLOB, and BFILE. These data types 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.
A temporary tablespace that resides on local storage and is accessible by a specific database instance. In contrast, a shared shared temporary tablespace resides on shared storage and is accessible by all database instances.
Within the context of globalization support, a linguistic and cultural environment in which a system or program is running.
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.
Reads and writes of buffers in the database buffer cache.
A read of a buffer in the database buffer cache.
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 virtual disk partition.
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.
A data corruption that occurs when the database thinks that it has written a block to persistent storage, but the block either was not written, or a previous version of the block was written.
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.
The part of a floating-point number that contains its significant digits.
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.
A schema object that stores the result of a query. Oracle materialized views can be read-only or updatable.
See also view.
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.
The rate of change in a cumulative statistic
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).
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.
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.
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.
Encrypting data as it travels across the network between a client and server.
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.
An RDBMS that implements object-oriented features such as user-defined types, inheritance, and polymorphism.
An special kind of table in which each row represents an object.
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.
An online redo log file and its redundant copies.
The minimum unit of data that the operating system can read or write.
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.
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.
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.
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.
The operating system location of an Oracle Database installation.
An integrated development environment (IDE) for building service-oriented applications using the latest industry standards for Java, XML, Web services, and SQL.
A standard, Java-compatible environment that runs any pure Java application.
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.
A database option that enables you to create multiple PDBs in a CDB.
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.
See Oracle RAC.
A feature for OLTP applications that enables distribution and replication of data across a pool of Oracle databases in a shared-nothing architecture. Applications access the pool as a single, logical database called a sharded database (SDB).
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.
A full-text retrieval technology integrated with Oracle Database.
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.
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.
A database administrator who manages one or more PDBs. A CDB administrator manages the whole CDB.
A compressed file that contains both PDB data files and an XML metadata file. You can create a PDB by specifying the archive file, and thereby avoid copying the XML file and the data files separately.
A security mechanism to restrict operations that are available to local users connected to a specified PDB.
Within a CDB, a restore point that usable only for a specific PDB. In contrast, a CDB restore point is usable by all PDBs.
The user-initiated update of the application in an application PDB to the latest version and patch in the application root.
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 specified share of system resources, CPU, parallel execution servers, and memory for a PDB or set of PDBs.
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.
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 logical grouping of related PL/SQL types, variables, and subprograms.
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.
A named PL/SQL block that can be invoked with a set of parameters
The transfer of data into the IM column store. Population does not insert new data into the database; rather, it brings existing data into memory and stores it in columnar format.
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.
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 WHERE condition in a SQL statement.
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 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.
The background process that detects the termination of other background processes. If a server or dispatcher process terminates abnormally, then the process monitor (PMON) group is responsible for performing process recovery.
The group of background processes that is responsible for the monitoring and cleanup of other processes. The PMON group includes process monitor (PMON), Cleanup Main Process (CLMN), and Cleanup Helper Processes (CLnn).
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.
A PDB that references a PDB in a remote CDB using a database link. The remote PDB is called a referenced PDB.
A column that is not stored in a table, yet behaves like a table column.
An operation that retrieves data from tables or views. For example, SELECT * FROM employees is a query.
A top-level SELECT statement, subquery, or unmerged view.
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 process of choosing the most efficient means of executing a SQL statement.
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.
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.
A database that is available for queries only and cannot be modified.
A database instance that cannot process DML and does not support client connections.
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.
A database instance that can process DML and supports direct client connections. By default, a database instance is read/write.
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. Recovery Appliance is an Oracle Engineered System specifically designed to protect Oracle databases. Integrated with RMAN, it enables a centralized, incremental-forever backup strategy for hundreds to thousands of databases across the enterprise, using cloud-scale, fully fault-tolerant hardware and storage.
A centralized backup repository located in an Oracle database. The recovery catalog contains metadata about RMAN backups.
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.
A partitioning strategy in which a child table is solely defined through the foreign key relationship with a parent table. For every partition in the parent table, exactly one corresponding partition exists in the child table.
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.
The PDB that is referenced by a proxy PDB. A local PDB is in the same CDB as its referenced PDB, whereas a remote PDB is in a different CDB.
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 read-only clone of a source PDB that can periodically synchronize with a source PDB. Depending on the value you specify in the REFRESH MODE clause of the CREATE PLUGGABLE DATABASE statement, the synchronization occurs either automatically or manually.
A set of tuples.
A database that conforms to the relational model, storing data in a set of simple relations.
A management system that moves data into a relational database, stores the data, and retrieves it so that applications can manipulate it.
The process of sharing database objects and data at multiple databases.
A memory area in the shared pool that Oracle Database can use to allocate large contiguous chunks of memory.
A container for resource plan directives that specify how resources are allocated to resource consumer groups.
A set of limits and controls for CPU, physical I/O, or logical I/O consumption for sessions in a consumer group.
A user-defined a name associated with an SCN of the database corresponding to the time of the creation of the restore point.
The set of data retrieved from execution of a SELECT statement.
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.
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 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.
A set of rows returned by a step in an execution plan.
An iterative control structure that processes a set of rows and produces a row set.
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 globally unique address for a row in a database.
A set of interlinked schemas that enable Oracle documentation and Oracle instructional materials to illustrate common database tasks.
A named SCN in a transaction to which the transaction can be rolled back.
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.
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).
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.
A server-side binary file containing initialization parameter settings that is read and written to by the database.
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.
A multitier architecture relying on services that support computer-to-computer interaction over a network.
System global area. A group of shared memory structures that contain data and control information for one Oracle database instance.
A single database participating in a sharding configuration.
A database that stores the sharded database (SDB) configuration data and provides other functionality, such as cross shard queries and centralized management.
In a sharding architecture, collection of shards that appear to applications as a single logical database.
A data tier architecture in which data is horizontally partitioned across independent databases. Sharding is a shared-nothing database architecture because shards do not share physical resources such as CPU, memory, or storage devices. Shards are also loosely coupled in terms of software; they do not run clusterware.
A partitioning key for a sharded table.
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.
A temporary tablespace that resides on shared storage and is accessible by all database instances. Starting in Oracle Database 12c Release 2 (12.2), temporary tablespaces are either shared or local. In previous releases, all temporary tablespaces were shared temporary tablespaces.
The use of a single set of undo data files for an entire CDB.
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.
A PDB that is cloned using the SNAPSHOT COPY clause. When creating a snapshot copy, Oracle Database does not make a complete copy of the source data files. Rather, Oracle Database creates a storage-level snapshot of the underlying file system, and then uses the snapshot to create PDB clones. Unlike a standard clone PDB, a snapshot copy PDB cannot be unplugged from the CDB root or plugged in to an application root.
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 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 session-level structure that contains metadata about the status of database resources such as processes, sessions, and transactions in the SGA.
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.
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.
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.
An event trigger caused by events such as error messages, or database instance startup and shutdown.
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 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 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.
An identifier is unique to a transaction and represents the undo segment number, slot, and sequence number.
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 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.
A self-contained set of PDB data files, and an XML metadata file that specifies the locations of the PDB files.
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.
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.
Hybrid Columnar Compression specified with COLUMN STORE COMPRESS FOR QUERY. This type of compression is useful in data warehouses.
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.