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Host Variables with Nonprimitive TypesManual ChaptersPG1834.4.4.3. Host Variables with Nonprimitive Types As a host variable you can also use arrays, typedefs, structs, and pointers.Host Variables with Nonprimitive Types Hot StandbyManual ChaptersPG1826.4. Hot Standby Hot standby is the term used to describe the ability to connect to the server and run read-only queries while the server is in archive recovery or standby mode. This is use…Hot Standby Hot Standby Parameter ReferenceManual ChaptersPG1826.4.4. Hot Standby Parameter Reference Various parameters have been mentioned above in Section 26.4.2 and Section 26.4.3. On the primary, the wal_level parameter can be used. max_standby_ar…Hot Standby Parameter Reference How Connections Are EstablishedManual ChaptersPG1851.2. How Connections Are Established PostgreSQL implements a “process per user” client/server model. In this model, every client process connects to exactly one backend process. As we do no…How Connections Are Established How Extensibility WorksManual ChaptersPG1836.1. How Extensibility Works PostgreSQL is extensible because its operation is catalog-driven. If you are familiar with standard relational database systems, you know that they store inform…How Extensibility Works How It WorksManual ChaptersPG18How It Works The basic idea is to have a replication start point from the source server and set up a logical replication to start from this point: Start the target server with the specified …How It Works How It WorksManual ChaptersPG18How It Works The basic idea is to copy all file system-level changes from the source cluster to the target cluster: Scan the WAL log of the target cluster, starting from the last checkpoint …How It Works How Parallel Query WorksManual ChaptersPG1815.1. How Parallel Query Works When the optimizer determines that parallel query is the fastest execution strategy for a particular query, it will create a query plan that includes a Gather …How Parallel Query Works How SELECT Rules WorkManual ChaptersPG1839.2.1. How SELECT Rules Work Rules ON SELECT are applied to all queries as the last step, even if the command given is an INSERT, UPDATE or DELETE. And they have different semantics from ru…How SELECT Rules Work How the Planner Uses StatisticsManual ChaptersPG18Chapter 69. How the Planner Uses Statistics This chapter builds on the material covered in Section 14.1 and Section 14.2 to show some additional details about how the planner uses the system…How the Planner Uses Statistics How to Use ItManual ChaptersPG18F.9.2. How to Use It Here's a simple example of usage: CREATE TABLE users ( nick CITEXT PRIMARY KEY, pass TEXT NOT NULL ); INSERT INTO users VALUES ( 'larry', sha256(random()::text::bytea) )…How to Use It How to Use ItManual ChaptersPG18F.21.2. How to Use It Here's a simple example of usage: CREATE TABLE image (title text, raster lo); CREATE TRIGGER t_raster BEFORE UPDATE OR DELETE ON image FOR EACH ROW EXECUTE FUNCTION lo_…How to Use It How Update Rules WorkManual ChaptersPG1839.4.1. How Update Rules Work Keep the syntax: CREATE [ OR REPLACE ] RULE name AS ON event TO table [ WHERE condition ] DO [ ALSO | INSTEAD ] { NOTHING | command | ( command ; command ... ) …How Update Rules Work hstore External RepresentationManual ChaptersPG18F.17.1. hstore External Representation The text representation of an hstore, used for input and output, includes zero or more key => value pairs separated by commas. Some examples: k => v fo…hstore External Representation hstore Operators and FunctionsManual ChaptersPG18F.17.2. hstore Operators and Functions The operators provided by the hstore module are shown in Table F.6, the functions in Table F.7. Table F.6. hstore Operators Operator Description Exampl…hstore Operators and Functions hstore — hstore key/value datatypeManual ChaptersPG18F.17. hstore — hstore key/value datatype This module implements the hstore data type for storing sets of key/value pairs within a single PostgreSQL value. This can be useful in various scena…hstore — hstore key/value datatype HTMLManual ChaptersPG18J.3.1. HTML To build the HTML version of the documentation: doc/src/sgml$ make html This is also the default target. The output appears in the subdirectory html. To produce HTML documentatio…HTML I/OManual ChaptersPG1819.4.5. I/O backend_flush_after (integer) # Whenever more than this amount of data has been written by a single backend, attempt to force the OS to issue these writes to the underlying stora…I/O ICU CollationsManual ChaptersPG1823.2.2.2.2. ICU Collations With ICU, it is not sensible to enumerate all possible locale names. ICU uses a particular naming system for locales, but there are many more ways to name a locale…ICU Collations ICU CollationsManual ChaptersPG1823.2.2.3.2. ICU Collations ICU collations can be created like: CREATE COLLATION german (provider = icu, locale = 'de-DE'); ICU locales are specified as a BCP 47 Language Tag, but can also ac…ICU Collations ICU Comparison LevelsManual ChaptersPG1823.2.3.1. ICU Comparison Levels Comparison of two strings (collation) in ICU is determined by a multi-level process, where textual features are grouped into "levels". Treatment of each level…ICU Comparison Levels ICU Custom CollationsManual ChaptersPG1823.2.3. ICU Custom Collations ICU allows extensive control over collation behavior by defining new collations with collation settings as a part of the language tag. These settings can modify…ICU Custom Collations ICU Locale NamesManual ChaptersPG1823.1.5.1. ICU Locale Names The ICU format for the locale name is a Language Tag. CREATE COLLATION mycollation1 (provider = icu, locale = 'ja-JP'); CREATE COLLATION mycollation2 (provider = i…ICU Locale Names ICU LocalesManual ChaptersPG1823.1.5. ICU LocalesICU Locales ICU Tailoring RulesManual ChaptersPG1823.2.3.4. ICU Tailoring Rules If the options provided by the collation settings shown above are not sufficient, the order of collation elements can be changed with tailoring rules, whose syn…ICU Tailoring Rules Ident AuthenticationManual ChaptersPG1820.8. Ident Authentication The ident authentication method works by obtaining the client's operating system user name from an ident server and using it as the allowed database user name (wit…Ident Authentication Identifiers and Key WordsManual ChaptersPG184.1.1. Identifiers and Key Words Tokens such as SELECT, UPDATE, or VALUES in the example above are examples of key words, that is, words that have a fixed meaning in the SQL language. The to…Identifiers and Key Words Identifying BugsManual ChaptersPG185.1. Identifying Bugs Before you report a bug, please read and re-read the documentation to verify that you can really do whatever it is you are trying. If it is not clear from the documenta…Identifying Bugs Identity ColumnsManual ChaptersPG185.3. Identity Columns An identity column is a special column that is generated automatically from an implicit sequence. It can be used to generate key values. To create an identity column, u…Identity Columns IF-THENManual ChaptersPG1841.6.4.1. IF-THEN IF boolean-expression THEN statements END IF; IF-THEN statements are the simplest form of IF. The statements between THEN and END IF will be executed if the condition is tr…IF-THEN IF-THEN-ELSEManual ChaptersPG1841.6.4.2. IF-THEN-ELSE IF boolean-expression THEN statements ELSE statements END IF; IF-THEN-ELSE statements add to IF-THEN by letting you specify an alternative set of statements that shoul…IF-THEN-ELSE IF-THEN-ELSIFManual ChaptersPG1841.6.4.3. IF-THEN-ELSIF IF boolean-expression THEN statements [ ELSIF boolean-expression THEN statements [ ELSIF boolean-expression THEN statements ... ] ] [ ELSE statements ] END IF; Someti…IF-THEN-ELSIF ifdef, ifndef, elif, else, and endif DirectivesManual ChaptersPG1834.9.3. ifdef, ifndef, elif, else, and endif Directives You can use the following directives to compile code sections conditionally: EXEC SQL ifdef name; # Checks a name and processes subseq…ifdef, ifndef, elif, else, and endif Directives ignore-cipher-failureManual ChaptersPG18F.26.3.8.12. ignore-cipher-failure Dangerous! Instructs pgcrypto to use an incorrect decryption algorithm matching the historical behavior prior to the fix for CVE-2026-14663, by completely …ignore-cipher-failure ImplementationManual ChaptersPG1865.1.4. Implementation This section covers B-Tree index implementation details that may be of use to advanced users. See src/backend/access/nbtree/README in the source distribution for a muc…Implementation ImplementationManual ChaptersPG1865.4.4. Implementation Internally, a GIN index contains a B-tree index constructed over keys, where each key is an element of one or more indexed items (a member of an array, for example) an…Implementation ImplementationManual ChaptersPG1865.2.4. ImplementationImplementation ImplementationManual ChaptersPG1865.6.2. Implementation There are four kinds of pages in a hash index: the meta page (page zero), which contains statically allocated control information; primary bucket pages; overflow pages…Implementation ImplementationManual ChaptersPG1865.3.4. Implementation This section covers implementation details and other tricks that are useful for implementers of SP-GiST operator classes to know.Implementation Implementation DetailsManual ChaptersPG188.7.4. Implementation Details Enum labels are case sensitive, so 'happy' is not the same as 'HAPPY'. White space in the labels is significant too. Although enum types are primarily intended …Implementation Details