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Add hooks for session start and session end
These hooks can be used in loadable modules. A simple test module is included. Discussion: https://postgr.es/m/20170720204733.40f2b7eb.nagata@sraoss.co.jp Fabrízio de Royes Mello and Yugo Nagata Reviewed by Michael Paquier and Aleksandr Parfenov
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‎src/backend/tcop/postgres.c

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@@ -169,6 +169,9 @@ static ProcSignalReason RecoveryConflictReason;
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static MemoryContext row_description_context = NULL;
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static StringInfoData row_description_buf;
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/* Hook for plugins to get control at start of session */
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session_start_hook_type session_start_hook = NULL;
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/* ----------------------------------------------------------------
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* decls for routines only used in this file
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* ----------------------------------------------------------------
@@ -3857,6 +3860,9 @@ PostgresMain(int argc, char *argv[],
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if (!IsUnderPostmaster)
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PgStartTime = GetCurrentTimestamp();
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if (session_start_hook)
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(*session_start_hook) ();
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/*
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* POSTGRES main processing loop begins here
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*

‎src/backend/utils/init/postinit.c

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@@ -76,6 +76,8 @@ static bool ThereIsAtLeastOneRole(void);
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static void process_startup_options(Port *port, bool am_superuser);
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static void process_settings(Oid databaseid, Oid roleid);
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/* Hook for plugins to get control at end of session */
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session_end_hook_type session_end_hook = NULL;
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/*** InitPostgres support ***/
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@@ -1154,6 +1156,10 @@ ShutdownPostgres(int code, Datum arg)
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* them explicitly.
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*/
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LockReleaseAll(USER_LOCKMETHOD, true);
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/* Hook at session end */
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if (session_end_hook)
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(*session_end_hook) ();
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}
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‎src/include/tcop/tcopprot.h

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@@ -35,6 +35,13 @@ extern PGDLLIMPORT const char *debug_query_string;
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extern int max_stack_depth;
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extern int PostAuthDelay;
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/* Hook for plugins to get control at start and end of session */
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typedef void (*session_start_hook_type) (void);
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typedef void (*session_end_hook_type) (void);
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extern PGDLLIMPORT session_start_hook_type session_start_hook;
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extern PGDLLIMPORT session_end_hook_type session_end_hook;
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/* GUC-configurable parameters */
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typedef enum

‎src/test/modules/Makefile

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@@ -15,6 +15,7 @@ SUBDIRS = \
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test_pg_dump \
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test_rbtree \
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test_rls_hooks \
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test_session_hooks \
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test_shm_mq \
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worker_spi
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‎src/test/modules/test_session_hooks/.gitignore

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# Generated subdirectories
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/log/
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/results/
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/tmp_check/

‎src/test/modules/test_session_hooks/Makefile

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# src/test/modules/test_session_hooks/Makefile
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MODULES = test_session_hooks
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PGFILEDESC = "test_session_hooks - Test session hooks with an extension"
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EXTENSION = test_session_hooks
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DATA = test_session_hooks--1.0.sql
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REGRESS = test_session_hooks
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REGRESS_OPTS = --temp-config=$(top_srcdir)/src/test/modules/test_session_hooks/session_hooks.conf
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ifdef USE_PGXS
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PG_CONFIG = pg_config
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PGXS := $(shell $(PG_CONFIG) --pgxs)
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include $(PGXS)
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else
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subdir = src/test/modules/test_session_hooks
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top_builddir = ../../../..
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include $(top_builddir)/src/Makefile.global
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include $(top_srcdir)/contrib/contrib-global.mk
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endif

‎src/test/modules/test_session_hooks/README

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test_session_hooks is an example of how to use session start and end
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hooks.

‎src/test/modules/test_session_hooks/expected/test_session_hooks.out

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CREATE ROLE regress_sess_hook_usr1 SUPERUSER LOGIN;
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CREATE ROLE regress_sess_hook_usr2 SUPERUSER LOGIN;
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\set prevdb :DBNAME
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\set prevusr :USER
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CREATE TABLE session_hook_log(id SERIAL, dbname TEXT, username TEXT, hook_at TEXT);
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SELECT * FROM session_hook_log ORDER BY id;
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id | dbname | username | hook_at
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----+--------+----------+---------
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(0 rows)
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\c :prevdb regress_sess_hook_usr1
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SELECT * FROM session_hook_log ORDER BY id;
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id | dbname | username | hook_at
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----+--------+----------+---------
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(0 rows)
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\c :prevdb regress_sess_hook_usr2
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SELECT * FROM session_hook_log ORDER BY id;
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id | dbname | username | hook_at
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----+--------------------+------------------------+---------
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1 | contrib_regression | regress_sess_hook_usr2 | START
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(1 row)
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\c :prevdb :prevusr
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SELECT * FROM session_hook_log ORDER BY id;
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id | dbname | username | hook_at
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----+--------------------+------------------------+---------
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1 | contrib_regression | regress_sess_hook_usr2 | START
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2 | contrib_regression | regress_sess_hook_usr2 | END
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(2 rows)
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‎src/test/modules/test_session_hooks/session_hooks.conf

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shared_preload_libraries = 'test_session_hooks'
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test_session_hooks.username = regress_sess_hook_usr2

‎src/test/modules/test_session_hooks/sql/test_session_hooks.sql

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CREATE ROLE regress_sess_hook_usr1 SUPERUSER LOGIN;
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CREATE ROLE regress_sess_hook_usr2 SUPERUSER LOGIN;
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\set prevdb :DBNAME
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\set prevusr :USER
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CREATE TABLE session_hook_log(id SERIAL, dbname TEXT, username TEXT, hook_at TEXT);
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SELECT * FROM session_hook_log ORDER BY id;
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\c :prevdb regress_sess_hook_usr1
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SELECT * FROM session_hook_log ORDER BY id;
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\c :prevdb regress_sess_hook_usr2
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SELECT * FROM session_hook_log ORDER BY id;
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\c :prevdb :prevusr
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SELECT * FROM session_hook_log ORDER BY id;

‎src/test/modules/test_session_hooks/test_session_hooks--1.0.sql

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/* src/test/modules/test_hook_session/test_hook_session--1.0.sql */
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-- complain if script is sourced in psql, rather than via CREATE EXTENSION
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\echo Use "CREATE EXTENSION test_hook_session" to load this file. \quit

‎src/test/modules/test_session_hooks/test_session_hooks.c

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/* -------------------------------------------------------------------------
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*
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* test_session_hooks.c
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* Code for testing SESSION hooks.
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*
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* Copyright (c) 2010-2017, PostgreSQL Global Development Group
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*
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* IDENTIFICATION
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* src/test/modules/test_session_hooks/test_session_hooks.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/xact.h"
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#include "commands/dbcommands.h"
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#include "executor/spi.h"
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#include "lib/stringinfo.h"
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#include "miscadmin.h"
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#include "tcop/tcopprot.h"
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#include "utils/snapmgr.h"
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#include "utils/builtins.h"
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PG_MODULE_MAGIC;
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/* Entry point of library loading/unloading */
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void _PG_init(void);
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void _PG_fini(void);
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/* GUC variables */
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static char *session_hook_username = "postgres";
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/* Original Hook */
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static session_start_hook_type prev_session_start_hook = NULL;
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static session_end_hook_type prev_session_end_hook = NULL;
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static void
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register_session_hook(const char *hook_at)
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{
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const char *username;
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StartTransactionCommand();
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SPI_connect();
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PushActiveSnapshot(GetTransactionSnapshot());
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username = GetUserNameFromId(GetUserId(), false);
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/* Register log just for configured username */
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if (!strcmp(username, session_hook_username))
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{
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const char *dbname;
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int ret;
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StringInfoData buf;
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dbname = get_database_name(MyDatabaseId);
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initStringInfo(&buf);
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appendStringInfo(&buf, "INSERT INTO session_hook_log (dbname, username, hook_at) ");
60+
appendStringInfo(&buf, "VALUES ('%s', '%s', '%s');",
61+
dbname, username, hook_at);
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ret = SPI_exec(buf.data, 0);
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if (ret != SPI_OK_INSERT)
65+
elog(ERROR, "SPI_execute failed: error code %d", ret);
66+
}
67+
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SPI_finish();
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PopActiveSnapshot();
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CommitTransactionCommand();
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}
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/* sample session start hook function */
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static void
75+
sample_session_start_hook()
76+
{
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/* Hook just normal backends */
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if (MyBackendId != InvalidBackendId)
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{
80+
(void) register_session_hook("START");
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if (prev_session_start_hook)
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prev_session_start_hook();
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}
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}
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/* sample session end hook function */
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static void
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sample_session_end_hook()
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{
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/* Hook just normal backends */
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if (MyBackendId != InvalidBackendId)
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{
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if (prev_session_end_hook)
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prev_session_end_hook();
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(void) register_session_hook("END");
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}
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}
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/*
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* Module Load Callback
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*/
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void
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_PG_init(void)
106+
{
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/* Save Hooks for Unload */
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prev_session_start_hook = session_start_hook;
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prev_session_end_hook = session_end_hook;
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/* Set New Hooks */
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session_start_hook = sample_session_start_hook;
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session_end_hook = sample_session_end_hook;
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/* Load GUCs */
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DefineCustomStringVariable("test_session_hooks.username",
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"Username to register log on session start or end",
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NULL,
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&session_hook_username,
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"postgres",
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PGC_SIGHUP,
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0, NULL, NULL, NULL);
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}
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/*
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* Module Unload Callback
127+
*/
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void
129+
_PG_fini(void)
130+
{
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/* Uninstall Hooks */
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session_start_hook = prev_session_start_hook;
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session_end_hook = prev_session_end_hook;
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}

‎src/test/modules/test_session_hooks/test_session_hooks.control

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comment = 'Test start/end hook session with an extension'
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default_version = '1.0'
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relocatable = true

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