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Add hooks for session start and session end, take two
These hooks can be used in loadable modules. A simple test module is included. The first attempt was done with cd8ce3a but we lacked handling for NO_INSTALLCHECK in the MSVC scripts (problem solved afterwards by 431f159) so the buildfarm got angry. This also fixes a couple of issues noticed upon review compared to the first attempt, so the code has slightly changed, resulting in a more simple test module. Author: Fabrízio de Royes Mello, Yugo Nagata Reviewed-by: Andrew Dunstan, Michael Paquier, Aleksandr Parfenov Discussion: https://postgr.es/m/20170720204733.40f2b7eb.nagata@sraoss.co.jp Discussion: https://postgr.es/m/20190823042602.GB5275@paquier.xyz
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‎src/backend/tcop/postgres.c

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@@ -171,6 +171,9 @@ 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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* ----------------------------------------------------------------
@@ -3968,6 +3971,9 @@ 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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@@ -78,6 +78,8 @@ 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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@@ -1195,6 +1197,10 @@ 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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@@ -30,6 +30,13 @@ 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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@@ -21,6 +21,7 @@ SUBDIRS = \
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test_predtest \
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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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unsafe_tests \
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worker_spi

‎src/test/modules/test_session_hooks/.gitignore

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@@ -0,0 +1,4 @@
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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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MODULE_big = test_session_hooks
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OBJS = test_session_hooks.o $(WIN32RES)
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PGFILEDESC = "test_session_hooks - tests for start and end session hooks"
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REGRESS = test_session_hooks
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REGRESS_OPTS = --temp-config=$(top_srcdir)/src/test/modules/test_session_hooks/session_hooks.conf
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# Disabled because these tests require extra configuration with
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# "shared_preload_libraries=test_session_hooks", which typical
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# installcheck users do not have (e.g. buildfarm clients).
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NO_INSTALLCHECK = 1
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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
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==================
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test_session_hooks is an example of how to use session start and end
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hooks.
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This module will insert into a pre-existing table called "session_hook_log"
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a log activity which happens at session start and end. It is possible
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to control which user information is logged when using the configuration
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parameter "test_session_hooks.username". If set, the hooks will log only
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information of the session user matching the parameter value.

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

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--
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-- Tests for start and end session hooks
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--
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-- Only activity from role regress_sess_hook_usr2 is logged.
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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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DROP ROLE regress_sess_hook_usr1;
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DROP ROLE regress_sess_hook_usr2;

‎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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--
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-- Tests for start and end session hooks
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--
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-- Only activity from role regress_sess_hook_usr2 is logged.
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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;
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DROP ROLE regress_sess_hook_usr1;
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DROP ROLE regress_sess_hook_usr2;

‎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 start and end session hooks.
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*
6+
* Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
7+
* Portions Copyright (c) 1994, Regents of the University of California
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*
9+
* IDENTIFICATION
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* src/test/modules/test_session_hooks/test_session_hooks.c
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*
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* -------------------------------------------------------------------------
13+
*/
14+
#include "postgres.h"
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16+
#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"
22+
#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 */
28+
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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/* Previous hooks on stack */
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static session_start_hook_type prev_session_start_hook = NULL;
36+
static session_end_hook_type prev_session_end_hook = NULL;
37+
38+
static void
39+
register_session_hook(const char *hook_at)
40+
{
41+
const char *username;
42+
43+
StartTransactionCommand();
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SPI_connect();
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PushActiveSnapshot(GetTransactionSnapshot());
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/* Check the current user validity */
48+
username = GetUserNameFromId(GetUserId(), false);
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/* Register log just for configured username */
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if (strcmp(username, session_hook_username) == 0)
52+
{
53+
const char *dbname;
54+
int ret;
55+
StringInfoData buf;
56+
57+
dbname = get_database_name(MyDatabaseId);
58+
59+
initStringInfo(&buf);
60+
61+
appendStringInfo(&buf, "INSERT INTO session_hook_log (dbname, username, hook_at) ");
62+
appendStringInfo(&buf, "VALUES (%s, %s, %s);",
63+
quote_literal_cstr(dbname),
64+
quote_literal_cstr(username),
65+
quote_literal_cstr(hook_at));
66+
67+
ret = SPI_exec(buf.data, 0);
68+
if (ret != SPI_OK_INSERT)
69+
elog(ERROR, "SPI_execute failed: error code %d", ret);
70+
}
71+
72+
SPI_finish();
73+
PopActiveSnapshot();
74+
CommitTransactionCommand();
75+
}
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/* sample session start hook function */
78+
static void
79+
sample_session_start_hook(void)
80+
{
81+
if (prev_session_start_hook)
82+
prev_session_start_hook();
83+
84+
/* consider only normal backends */
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if (MyBackendId == InvalidBackendId)
86+
return;
87+
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/* consider backends connected to a database */
89+
if (!OidIsValid(MyDatabaseId))
90+
return;
91+
92+
register_session_hook("START");
93+
}
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95+
/* sample session end hook function */
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static void
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sample_session_end_hook(void)
98+
{
99+
if (prev_session_end_hook)
100+
prev_session_end_hook();
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/* consider only normal backends */
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if (MyBackendId == InvalidBackendId)
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return;
105+
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/* consider backends connected to a database */
107+
if (!OidIsValid(MyDatabaseId))
108+
return;
109+
110+
register_session_hook("END");
111+
}
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/*
114+
* Module load callback
115+
*/
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void
117+
_PG_init(void)
118+
{
119+
/* Save previous hooks */
120+
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 */
128+
DefineCustomStringVariable("test_session_hooks.username",
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"Username to register log on session start or end",
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NULL,
131+
&session_hook_username,
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"postgres",
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PGC_SIGHUP,
134+
0, NULL, NULL, NULL);
135+
}
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/*
138+
* Module unload callback
139+
*/
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void
141+
_PG_fini(void)
142+
{
143+
/* Uninstall hooks */
144+
session_start_hook = prev_session_start_hook;
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session_end_hook = prev_session_end_hook;
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}

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