Atomicity, Consistency, Isolation, and Durability. This set of properties of database transactions is intended to guarantee validity in concurrent operation and even in event of errors, power failures, etc.

A function that combines (aggregates) multiple input values, for example by counting, averaging or adding, yielding a single output value.

For more information, see Section 9.21.

See Also Window function (routine).

The process of collecting statistics from data in tables and other relations to help the query planner to make decisions about how to execute queries.

(Don't confuse this term with the ANALYZE option to the EXPLAIN command.)

For more information, see ANALYZE.

In reference to a datum: the fact that its value cannot be broken down into smaller components.

In reference to a database transaction: see atomicity.

The property of a transaction that either all its operations complete as a single unit or none do. In addition, if a system failure occurs during the execution of a transaction, no partial results are visible after recovery. This is one of the ACID properties.

An element with a certain name and data type found within a tuple.

A set of background processes that routinely perform vacuum and analyze operations.

For more information, see Section 25.1.6.

Process of an instance which acts on behalf of a client session and handles its requests.

(Don't confuse this term with the similar terms Background Worker or Background Writer).

Process within an instance, which runs system- or user-supplied code. Serves as infrastructure for several features in PostgreSQL, such as logical replication and parallel queries. In addition, Extensions can add custom background worker processes.

For more information, see Chapter 48.

A process that writes dirty data pages from shared memory to the file system. It wakes up periodically, but works only for a short period in order to distribute its expensive I/O activity over time to avoid generating larger I/O peaks which could block other processes.

For more information, see Section 20.4.5.

A binary copy of all database cluster files. It is generated by the tool pg_basebackup. In combination with WAL files it can be used as the starting point for recovery, log shipping, or streaming replication.

Space in data pages which does not contain current row versions, such as unused (free) space or outdated row versions.

A conversion of a datum from its current data type to another data type.

For more information, see CREATE CAST.

The SQL standard uses this term to indicate what is called a database in PostgreSQL's terminology.

(Don't confuse this term with