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Transaction ID and Snapshot Information FunctionsManual ChaptersPG189.27.8. Transaction ID and Snapshot Information Functions The functions shown in Table 9.84 provide server transaction information in an exportable form. The main use of these functions is t…Transaction ID and Snapshot Information Functions Transaction IsolationManual ChaptersPG1813.2. Transaction Isolation The SQL standard defines four levels of transaction isolation. The most strict is Serializable, which is defined by the standard in a paragraph which says that an…Transaction Isolation Transaction ManagementManual ChaptersPG1841.8. Transaction Management In procedures invoked by the CALL command as well as in anonymous code blocks (DO command), it is possible to end transactions using the commands COMMIT and ROLL…Transaction Management Transaction ManagementManual ChaptersPG1844.8. Transaction Management In a procedure called from the top level or an anonymous code block (DO command) called from the top level it is possible to control transactions. To commit the …Transaction Management Transaction ManagementManual ChaptersPG1842.10. Transaction Management In a procedure called from the top level or an anonymous code block (DO command) called from the top level it is possible to control transactions. To commit the…Transaction Management Transaction ManagementManual ChaptersPG18F.38.4. Transaction Management During a query that references any remote tables on a foreign server, postgres_fdw opens a transaction on the remote server if one is not already open correspo…Transaction Management Transaction ManagementManual ChaptersPG1845.4. Transaction Management It is not possible to run transaction control commands such as COMMIT and ROLLBACK through SPI functions such as SPI_execute. There are, however, separate interf…Transaction Management Transaction Management OptionsManual ChaptersPG18F.38.1.6. Transaction Management Options As described in the Transaction Management section, in postgres_fdw transactions are managed by creating corresponding remote transactions, and subtr…Transaction Management Options Transaction Prepare CallbackManual ChaptersPG1847.6.4.11. Transaction Prepare Callback The required prepare_cb callback is called whenever a transaction which is prepared for two-phase commit has been decoded. The change_cb callback for …Transaction Prepare Callback Transaction ProcessingManual ChaptersPG18Chapter 67. Transaction Processing This chapter provides an overview of the internals of PostgreSQL's transaction management system. The word transaction is often abbreviated as xact.Transaction Processing Transaction Rollback Prepared CallbackManual ChaptersPG1847.6.4.13. Transaction Rollback Prepared Callback The required rollback_prepared_cb callback is called whenever a transaction ROLLBACK PREPARED has been decoded. The gid field, which is part…Transaction Rollback Prepared Callback TransactionsManual ChaptersPG183.4. Transactions Transactions are a fundamental concept of all database systems. The essential point of a transaction is that it bundles multiple steps into a single, all-or-nothing operati…Transactions Transactions and IdentifiersManual ChaptersPG1867.1. Transactions and Identifiers Transactions can be created explicitly using BEGIN or START TRANSACTION and ended using COMMIT or ROLLBACK. SQL statements outside of explicit transactions…Transactions and Identifiers Transactions and LockingManual ChaptersPG1867.2. Transactions and Locking The transaction IDs of currently executing transactions are shown in pg_locks in columns virtualxid and transactionid. Read-only transactions will have virtual…Transactions and Locking Transformation ProcessManual ChaptersPG1851.3.2. Transformation Process The parser stage creates a parse tree using only fixed rules about the syntactic structure of SQL. It does not make any lookups in the system catalogs, so ther…Transformation Process TransformsManual ChaptersPG188.14.6. Transforms Additional extensions are available that implement transforms for the jsonb type for different procedural languages. The extensions for PL/Perl are called jsonb_plperl and…Transforms TransformsManual ChaptersPG18F.17.7. Transforms Additional extensions are available that implement transforms for the hstore type for the languages PL/Perl and PL/Python. The extensions for PL/Perl are called hstore_plp…Transforms transformsManual ChaptersPG1835.55. transforms The view transforms contains information about the transforms defined in the current database. More precisely, it contains a row for each function contained in a transform …transforms TransformsManual ChaptersPG18F.22.5. Transforms The ltree_plpython3u extension implements transforms for the ltree type for PL/Python. If installed and specified when creating a function, ltree values are mapped to Pyth…Transforms Trapping ErrorsManual ChaptersPG1841.6.8. Trapping Errors By default, any error occurring in a PL/pgSQL function aborts execution of the function and the surrounding transaction. You can trap errors and recover from them by …Trapping Errors Trapping ErrorsManual ChaptersPG1844.6.2. Trapping Errors Functions accessing the database might encounter errors, which will cause them to abort and raise an exception. Both plpy.execute and plpy.prepare can raise an instan…Trapping Errors Trigger FunctionsManual ChaptersPG189.29. Trigger Functions While many uses of triggers involve user-written trigger functions, PostgreSQL provides a few built-in trigger functions that can be used directly in user-defined tri…Trigger Functions Trigger FunctionsManual ChaptersPG1841.10. Trigger Functions PL/pgSQL can be used to define trigger functions on data changes or database events. A trigger function is created with the CREATE FUNCTION command, declaring it as …Trigger Functions Trigger FunctionsManual ChaptersPG1844.5. Trigger Functions When a function is used as a trigger, the dictionary TD contains trigger-related values: TD["event"] contains the event as a string: INSERT, UPDATE, DELETE, or TRUNCA…Trigger Functions Trigger Functions in PL/TclManual ChaptersPG1842.6. Trigger Functions in PL/Tcl Trigger functions can be written in PL/Tcl. PostgreSQL requires that a function that is to be called as a trigger must be declared as a function with no arg…Trigger Functions in PL/Tcl triggered_update_columnsManual ChaptersPG1835.56. triggered_update_columns For triggers in the current database that specify a column list (like UPDATE OF column1, column2), the view triggered_update_columns identifies these columns.…triggered_update_columns triggersManual ChaptersPG1835.57. triggers The view triggers contains all triggers defined in the current database on tables and views that the current user owns or has some privilege other than SELECT on. Table 35.55…triggers TriggersManual ChaptersPG18Chapter 37. Triggers This chapter provides general information about writing trigger functions. Trigger functions can be written in most of the available procedural languages, including PL/p…Triggers Triggers for Automatic UpdatesManual ChaptersPG1812.4.3. Triggers for Automatic Updates Note The method described in this section has been obsoleted by the use of stored generated columns, as described in Section 12.2.2. When using a separ…Triggers for Automatic Updates Triggers on Data ChangesManual ChaptersPG1841.10.1. Triggers on Data Changes A data change trigger is declared as a function with no arguments and a return type of trigger. Note that the function must be declared with no arguments ev…Triggers on Data Changes Triggers on EventsManual ChaptersPG1841.10.2. Triggers on Events PL/pgSQL can be used to define event triggers. PostgreSQL requires that a function that is to be called as an event trigger must be declared as a function with no…Triggers on Events Trigram (or Trigraph) ConceptsManual ChaptersPG18F.35.1. Trigram (or Trigraph) Concepts A trigram is a group of three consecutive characters taken from a string. We can measure the similarity of two strings by counting the number of trigra…Trigram (or Trigraph) Concepts Truncatability OptionsManual ChaptersPG18F.38.1.8. Truncatability Options By default all foreign tables using postgres_fdw are assumed to be truncatable. This may be overridden using the following option: truncatable (boolean) This…Truncatability Options TRUNCATEManual ChaptersPG18TRUNCATE TRUNCATE — empty a table or set of tables Synopsis TRUNCATE [ TABLE ] [ ONLY ] name [ * ] [, ... ] [ RESTART IDENTITY | CONTINUE IDENTITY ] [ CASCADE | RESTRICT ]TRUNCATE Truncate CallbackManual ChaptersPG1847.6.4.6. Truncate Callback The optional truncate_cb callback is called for a TRUNCATE command. typedef void (*LogicalDecodeTruncateCB) (struct LogicalDecodingContext *ctx, ReorderBufferTXN …Truncate Callback Truncating a Large ObjectManual ChaptersPG1833.3.9. Truncating a Large Object To truncate a large object to a given length, call int lo_truncate(PGconn *conn, int fd, size_t len); This function truncates the large object descriptor fd…Truncating a Large Object Trust AuthenticationManual ChaptersPG1820.4. Trust Authentication When trust authentication is specified, PostgreSQL assumes that anyone who can connect to the server is authorized to access the database with whatever database us…Trust Authentication Trusted and Untrusted PL/PerlManual ChaptersPG1843.5. Trusted and Untrusted PL/Perl Normally, PL/Perl is installed as a “trusted” programming language named plperl. In this setup, certain Perl operations are disabled to preserve security.…Trusted and Untrusted PL/Perl Trusted ProceduresManual ChaptersPG18F.40.5.4. Trusted Procedures Trusted procedures are similar to security definer functions or setuid commands. SELinux provides a feature to allow trusted code to run using a security label d…Trusted Procedures tsm_system_rows — the SYSTEM_ROWS sampling method for TABLESAMPLEManual ChaptersPG18F.46. tsm_system_rows — the SYSTEM_ROWS sampling method for TABLESAMPLE The tsm_system_rows module provides the table sampling method SYSTEM_ROWS, which can be used in the TABLESAMPLE clause…tsm_system_rows — the SYSTEM_ROWS sampling method for TABLESAMPLE