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introduce new class (catalog) pg_variable
This table holds metadata about session variables created by command CREATE VARIABLE, and dropped by command DROP VARIABLE.
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‎doc/src/sgml/catalogs.sgml‎

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@@ -369,6 +369,11 @@
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<entry><link linkend="catalog-pg-user-mapping"><structname>pg_user_mapping</structname></link></entry>
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<entry>mappings of users to foreign servers</entry>
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</row>
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<row>
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<entry><link linkend="catalog-pg-variable"><structname>pg_variable</structname></link></entry>
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<entry>session variables</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
@@ -9834,4 +9839,132 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</replaceable>:<replaceable>&l
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</table>
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</sect1>
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<sect1 id="catalog-pg-variable">
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<title><structname>pg_variable</structname></title>
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<indexterm zone="catalog-pg-variable">
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<primary>pg_variable</primary>
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</indexterm>
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<para>
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The catalog <structname>pg_variable</structname> stores information about
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session variables.
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</para>
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<table>
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<title><structname>pg_variable</structname> Columns</title>
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<tgroup cols="1">
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<thead>
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<row>
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<entry role="catalog_table_entry"><para role="column_definition">
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Column Type
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</para>
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<para>
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Description
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</para></entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry role="catalog_table_entry"><para role="column_definition">
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<structfield>oid</structfield> <type>oid</type>
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</para>
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<para>
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Row identifier
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</para></entry>
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</row>
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<row>
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<entry role="catalog_table_entry"><para role="column_definition">
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<structfield>vartype</structfield> <type>oid</type>
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(references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
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</para>
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<para>
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The OID of the variable's data type
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</para></entry>
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</row>
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<row>
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<entry role="catalog_table_entry"><para role="column_definition">
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<structfield>varcreate_lsn</structfield> <type>pg_lsn</type>
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</para>
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<para>
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LSN of the transaction where the variable was created.
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<structfield>varcreate_lsn</structfield> and
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<structfield>oid</structfield> together form the all-time unique
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identifier (<structfield>oid</structfield> alone is not enough, since
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object identifiers can get reused).
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</para></entry>
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</row>
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<row>
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<entry role="catalog_table_entry"><para role="column_definition">
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<structfield>varname</structfield> <type>name</type>
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</para>
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<para>
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Name of the session variable
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</para></entry>
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</row>
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<row>
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<entry role="catalog_table_entry"><para role="column_definition">
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<structfield>varnamespace</structfield> <type>oid</type>
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(references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>oid</structfield>)
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</para>
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<para>
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The OID of the namespace that contains this variable
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</para></entry>
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</row>
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<row>
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<entry role="catalog_table_entry"><para role="column_definition">
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<structfield>varowner</structfield> <type>oid</type>
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(references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
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</para>
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<para>
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Owner of the variable
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</para></entry>
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</row>
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<row>
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<entry role="catalog_table_entry"><para role="column_definition">
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<structfield>vartypmod</structfield> <type>int4</type>
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</para>
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<para>
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<structfield>vartypmod</structfield> records type-specific data
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supplied at variable creation time (for example, the maximum
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length of a <type>varchar</type> column). It is passed to
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type-specific input functions and length coercion functions.
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The value will generally be -1 for types that do not need <structfield>vartypmod</structfield>.
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</para></entry>
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</row>
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<row>
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<entry role="catalog_table_entry"><para role="column_definition">
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<structfield>varcollation</structfield> <type>oid</type>
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(references <link linkend="catalog-pg-collation"><structname>pg_collation</structname></link>.<structfield>oid</structfield>)
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</para>
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<para>
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The defined collation of the variable, or zero if the variable is
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not of a collatable data type.
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</para></entry>
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</row>
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<row>
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<entry role="catalog_table_entry"><para role="column_definition">
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<structfield>varacl</structfield> <type>aclitem[]</type>
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</para>
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<para>
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Access privileges; see
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<xref linkend="sql-grant"/> and
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<xref linkend="sql-revoke"/>
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for details
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</para></entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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</sect1>
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</chapter>

‎src/backend/catalog/Makefile‎

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Original file line numberDiff line numberDiff line change
@@ -45,6 +45,7 @@ OBJS = \
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pg_shdepend.o \
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pg_subscription.o \
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pg_type.o \
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pg_variable.o \
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storage.o \
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toasting.o
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‎src/backend/catalog/meson.build‎

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@@ -32,6 +32,7 @@ backend_sources += files(
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'pg_shdepend.c',
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'pg_subscription.c',
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'pg_type.c',
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'pg_variable.c',
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'storage.c',
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'toasting.c',
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)

‎src/backend/catalog/pg_variable.c‎

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/*-------------------------------------------------------------------------
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*
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* pg_variable.c
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* session variables
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*
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* Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* IDENTIFICATION
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* src/backend/catalog/pg_variable.c
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include "access/heapam.h"
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#include "catalog/dependency.h"
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#include "catalog/indexing.h"
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#include "catalog/namespace.h"
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#include "catalog/objectaccess.h"
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#include "catalog/pg_collation.h"
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#include "catalog/pg_namespace.h"
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#include "catalog/pg_variable.h"
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#include "utils/builtins.h"
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#include "utils/pg_lsn.h"
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#include "utils/syscache.h"
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/*
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* Creates entry in pg_variable table
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*/
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ObjectAddress
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create_variable(const char *varName,
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Oid varNamespace,
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Oid varType,
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int32 varTypmod,
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Oid varOwner,
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Oid varCollation,
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bool if_not_exists)
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{
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NameData varname;
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bool nulls[Natts_pg_variable];
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Datum values[Natts_pg_variable];
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Relation rel;
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HeapTuple tup;
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TupleDesc tupdesc;
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ObjectAddress myself,
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referenced;
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ObjectAddresses *addrs;
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Oid varid;
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Assert(varName);
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Assert(OidIsValid(varNamespace));
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Assert(OidIsValid(varType));
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Assert(OidIsValid(varOwner));
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rel = table_open(VariableRelationId, RowExclusiveLock);
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/*
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* Check for duplicates. Note that this does not really prevent
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* duplicates, it's here just to provide nicer error message in common
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* case. The real protection is the unique key on the catalog.
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*/
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if (SearchSysCacheExists2(VARIABLENAMENSP,
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PointerGetDatum(varName),
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ObjectIdGetDatum(varNamespace)))
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{
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if (if_not_exists)
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ereport(NOTICE,
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(errcode(ERRCODE_DUPLICATE_OBJECT),
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errmsg("session variable \"%s\" already exists, skipping",
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varName)));
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else
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ereport(ERROR,
75+
(errcode(ERRCODE_DUPLICATE_OBJECT),
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errmsg("session variable \"%s\" already exists",
77+
varName)));
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table_close(rel, RowExclusiveLock);
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return InvalidObjectAddress;
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}
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memset(values, 0, sizeof(values));
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memset(nulls, false, sizeof(nulls));
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namestrcpy(&varname, varName);
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varid = GetNewOidWithIndex(rel, VariableOidIndexId, Anum_pg_variable_oid);
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values[Anum_pg_variable_oid - 1] = ObjectIdGetDatum(varid);
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values[Anum_pg_variable_varcreate_lsn - 1] = LSNGetDatum(GetXLogInsertRecPtr());
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values[Anum_pg_variable_varname - 1] = NameGetDatum(&varname);
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values[Anum_pg_variable_varnamespace - 1] = ObjectIdGetDatum(varNamespace);
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values[Anum_pg_variable_vartype - 1] = ObjectIdGetDatum(varType);
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values[Anum_pg_variable_vartypmod - 1] = Int32GetDatum(varTypmod);
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values[Anum_pg_variable_varowner - 1] = ObjectIdGetDatum(varOwner);
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values[Anum_pg_variable_varcollation - 1] = ObjectIdGetDatum(varCollation);
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nulls[Anum_pg_variable_varacl - 1] = true;
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tupdesc = RelationGetDescr(rel);
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tup = heap_form_tuple(tupdesc, values, nulls);
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CatalogTupleInsert(rel, tup);
106+
Assert(OidIsValid(varid));
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addrs = new_object_addresses();
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ObjectAddressSet(myself, VariableRelationId, varid);
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/* dependency on namespace */
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ObjectAddressSet(referenced, NamespaceRelationId, varNamespace);
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add_exact_object_address(&referenced, addrs);
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/* dependency on used type */
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ObjectAddressSet(referenced, TypeRelationId, varType);
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add_exact_object_address(&referenced, addrs);
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/* dependency on collation */
121+
if (OidIsValid(varCollation) &&
122+
varCollation != DEFAULT_COLLATION_OID)
123+
{
124+
ObjectAddressSet(referenced, CollationRelationId, varCollation);
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add_exact_object_address(&referenced, addrs);
126+
}
127+
128+
record_object_address_dependencies(&myself, addrs, DEPENDENCY_NORMAL);
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free_object_addresses(addrs);
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/* dependency on owner */
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recordDependencyOnOwner(VariableRelationId, varid, varOwner);
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/* dependency on extension */
135+
recordDependencyOnCurrentExtension(&myself, false);
136+
137+
heap_freetuple(tup);
138+
139+
/* post creation hook for new function */
140+
InvokeObjectPostCreateHook(VariableRelationId, varid, 0);
141+
142+
table_close(rel, RowExclusiveLock);
143+
144+
return myself;
145+
}
146+
147+
/*
148+
* Drop variable by OID
149+
*/
150+
void
151+
DropVariableById(Oid varid)
152+
{
153+
Relation rel;
154+
HeapTuple tup;
155+
156+
rel = table_open(VariableRelationId, RowExclusiveLock);
157+
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tup = SearchSysCache1(VARIABLEOID, ObjectIdGetDatum(varid));
159+
160+
if (!HeapTupleIsValid(tup))
161+
elog(ERROR, "cache lookup failed for variable %u", varid);
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163+
CatalogTupleDelete(rel, &tup->t_self);
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ReleaseSysCache(tup);
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table_close(rel, RowExclusiveLock);
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}

‎src/include/catalog/Makefile‎

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@@ -81,7 +81,8 @@ CATALOG_HEADERS := \
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pg_publication_namespace.h \
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pg_publication_rel.h \
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pg_subscription.h \
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pg_subscription_rel.h
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pg_subscription_rel.h \
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pg_variable.h
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GENERATED_HEADERS := $(CATALOG_HEADERS:%.h=%_d.h)
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‎src/include/catalog/meson.build‎

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@@ -69,6 +69,7 @@ catalog_headers = [
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'pg_publication_rel.h',
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'pg_subscription.h',
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'pg_subscription_rel.h',
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'pg_variable.h',
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]
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# The .dat files we need can just be listed alphabetically.

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