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Free Space MapManual ChaptersPG1866.3. Free Space Map Each heap and index relation, except for hash indexes, has a Free Space Map (FSM) to keep track of available space in the relation. It's stored alongside the main relati…Free Space Map FreezingManual ChaptersPG1819.10.4. Freezing To maintain correctness even after transaction IDs wrap around, PostgreSQL marks rows that are sufficiently old as frozen. These rows are visible to everyone; other transac…Freezing frkn_avgExtensionsExtensionsC aggregate extension providing my_avg for bigint and floating-point inputs. aggregate average Aggregate-Average Functions and aggregatesFunctions and aggregates · Extensions FROMSQL CommandsPG187.2.1. The FROM Clause # The FROM clause derives a table from one or more other tables given in a comma-separated table reference list. FROM table_reference [, table_reference [, ...]] A tab…Table Expressions › The FROM Clause FROM ClauseManual ChaptersPG18FROM Clause The FROM clause specifies one or more source tables for the SELECT. If multiple sources are specified, the result is the Cartesian product (cross join) of all the sources. But us…FROM Clause from_collapse_limitConfigurationReferencefrom_collapse_limit Query Tuning 10 The planner will merge sub-queries into upper queries if the resulting FROM list would have no more than this many items. Smaller values reduce planning t…Configuration · Query Tuning Frontend/Backend ProtocolManual ChaptersPG18Chapter 54. Frontend/Backend Protocol PostgreSQL uses a message-based protocol for communication between frontends and backends (clients and servers). The protocol is supported over TCP/IP a…Frontend/Backend Protocol frozenidWait EventsReferencefrozenid Lock 10 Waiting to update pg_database.datfrozenxid and pg_database.datminmxid. 11 12 13 14 15 16 17 18 19 20 9.6 Sub-second handoff during ordinary writes or planned DDL can be norm…Wait Events · Lock fsmExtensionsExtensionsTrigger-enforced finite state machines for application tables. fsm workflow state-machine trigger pg_fsm FeaturesFeatures · Extensions fsm_coreExtensionsExtensionsFinite state machine toolkit for PostgreSQL fsm workflow fsm_core FeaturesFeatures · Extensions fspg_ec_advisorExtensionsExtensionsSQL-based workload and resource scaling advisor for PostgreSQL 17 workload analysis capacity planning fspg_ec_advisor MonitoringMonitoring · Extensions fsyncConfigurationReferencefsync Write-Ahead Log 10 If this parameter is on, the PostgreSQL server will try to make sure that updates are physically written to disk, by issuing fsync() system calls or various equivale…Configuration · Write-Ahead Log ftreeExtensionsExtensionsatree extension for postgresql postgresql postgresql-extension ftree FeaturesFeatures · Extensions Full Text SearchManual ChaptersPG18Chapter 12. Full Text SearchFull Text Search full_page_writesConfigurationReferencefull_page_writes Write-Ahead Log 10 When this parameter is on, the PostgreSQL server writes the entire content of each disk page to WAL during the first modification of that page after a che…Configuration · Write-Ahead Log Function CallManual ChaptersPG1854.2.5. Function Call The Function Call sub-protocol allows the client to request a direct call of any function that exists in the database's pg_proc system catalog. The client must have exe…Function Call Function CallsManual ChaptersPG184.2.6. Function Calls The syntax for a function call is the name of a function (possibly qualified with a schema name), followed by its argument list enclosed in parentheses: function_name (…Function Calls Function Calls in FROMManual ChaptersPG18Function Calls in FROM PostgreSQL allows a function call to be written directly as a member of the FROM list. In the SQL standard it would be necessary to wrap such a function call in a sub-…Function Calls in FROM Function Optimization InformationManual ChaptersPG1836.11. Function Optimization Information By default, a function is just a “black box” that the database system knows very little about the behavior of. However, that means that queries using…Function Optimization Information Function OverloadingManual ChaptersPG1836.6. Function Overloading More than one function can be defined with the same SQL name, so long as the arguments they take are different. In other words, function names can be overloaded. W…Function Overloading Function SecurityManual ChaptersPG1821.6. Function Security Functions, triggers and row-level security policies allow users to insert code into the backend server that other users might execute unintentionally. Hence, these me…Function Security Function Volatility CategoriesManual ChaptersPG1836.7. Function Volatility Categories Every function has a volatility classification, with the possibilities being VOLATILE, STABLE, or IMMUTABLE. VOLATILE is the default if the CREATE FUNCTI…Function Volatility Categories Functional DependenciesManual ChaptersPG1869.2.1. Functional Dependencies Multivariate correlation can be demonstrated with a very simple data set — a table with two columns, both containing the same values: CREATE TABLE t (a INT, b…Functional Dependencies Functional DependenciesManual ChaptersPG1814.2.2.1. Functional Dependencies The simplest kind of extended statistics tracks functional dependencies, a concept used in definitions of database normal forms. We say that column b is fun…Functional Dependencies Functional DependenciesManual ChaptersPG18Functional Dependencies PostgreSQL recognizes functional dependency (allowing columns to be omitted from GROUP BY) only when a table's primary key is included in the GROUP BY list. The SQL s…Functional Dependencies FunctionsManual ChaptersPG18F.1.1. Functions bt_index_check(index regclass, heapallindexed boolean, checkunique boolean) returns void bt_index_check tests that its target, a B-Tree index, respects a variety of invarian…Functions FunctionsManual ChaptersPG18F.18.1. Functions The aggregator is an aggregate function int_array_aggregate(integer) that produces an integer array containing exactly the integers it is fed. This is a wrapper around arra…Functions FunctionsManual ChaptersPG18F.27.1. Functions pg_freespace(rel regclass IN, blkno bigint IN) returns int2 Returns the amount of free space on the page of the relation, specified by blkno, according to the FSM. pg_frees…Functions FunctionsManual ChaptersPG18F.28.1. Functions pg_get_logical_snapshot_meta(filename text) returns record # Gets logical snapshot metadata about a snapshot file that is located in the server's pg_logical/snapshots direc…Functions FunctionsManual ChaptersPG18F.30.1. Functions pg_prewarm(regclass, mode text default 'buffer', fork text default 'main', first_block int8 default null, last_block int8 default null) RETURNS int8 The first argument is t…Functions FunctionsManual ChaptersPG18F.32.3. Functions pg_stat_statements_reset(userid Oid, dbid Oid, queryid bigint, minmax_only boolean) returns timestamp with time zone pg_stat_statements_reset discards statistics gathered s…Functions FunctionsManual ChaptersPG18F.33.1. Functions pgstattuple(regclass) returns record pgstattuple returns a relation's physical length, percentage of “dead” tuples, and other info. This may help users to determine whether…Functions FunctionsManual ChaptersPG18F.34.1. Functions heap_force_kill(regclass, tid[]) returns void heap_force_kill marks “used” line pointers as “dead” without examining the tuples. The intended use of this function is to for…Functions FunctionsManual ChaptersPG18F.36.1. Functions pg_visibility_map(relation regclass, blkno bigint, all_visible OUT boolean, all_frozen OUT boolean) returns record Returns the all-visible and all-frozen bits in the visibi…Functions FunctionsManual ChaptersPG18F.38.2. Functions postgres_fdw_get_connections( IN check_conn boolean DEFAULT false, OUT server_name text, OUT user_name text, OUT valid boolean, OUT used_in_xact boolean, OUT closed boolean…Functions FunctionsManual ChaptersPG18E.6.3.4. Functions Add function casefold() to allow for more sophisticated case-insensitive matching (Jeff Davis) § This allows more accurate comparisons, i.e., a character can have multiple…Functions FunctionsManual ChaptersPG1810.3. Functions The specific function that is referenced by a function call is determined using the following procedure. Function Type Resolution Select the functions to be considered from t…Functions FunctionsManual ChaptersPG18F.48.3. Functions The unaccent() function removes accents (diacritic signs) from a given string. Basically, it's a wrapper around unaccent-type dictionaries, but it can be used outside norma…Functions Functions and OperatorsManual ChaptersPG18Chapter 9. Functions and Operators PostgreSQL provides a large number of functions and operators for the built-in data types. This chapter describes most of them, although additional special…Functions and Operators Functions and OperatorsManual ChaptersPG18F.20.3. Functions and Operators The isn module provides the standard comparison operators, plus B-tree and hash indexing support for all these data types. In addition, there are several spec…Functions and Operators