Back out the session_start and session_end hooks feature.

It's become apparent during testing that there are problems with at
least the testing regime. I don't think we should have it without a
working test regime, and the difficulties might indicate implementation
problems anyway, so I'm backing out the whole thing until that's sorted
out.

This reverts commits 74594842 9989f92a cd8ce3a2

src/backend/tcop/postgres.c

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

src/backend/utils/init/postinit.c

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

src/include/tcop/tcopprot.h

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

src/test/modules/Makefile

@@ -15,7 +15,6 @@ SUBDIRS = \
 		  test_pg_dump \
 		  test_rbtree \
 		  test_rls_hooks \
-		  test_session_hooks \
 		  test_shm_mq \
 		  worker_spi
 

src/test/modules/test_session_hooks/.gitignore

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

src/test/modules/test_session_hooks/Makefile

-# src/test/modules/test_session_hooks/Makefile
-
-MODULES = test_session_hooks
-PGFILEDESC = "test_session_hooks - Test session hooks with an extension"
-
-EXTENSION = test_session_hooks
-DATA = test_session_hooks--1.0.sql
-
-REGRESS = test_session_hooks
-REGRESS_OPTS = --temp-config=$(top_srcdir)/src/test/modules/test_session_hooks/session_hooks.conf
-
-ifdef USE_PGXS
-PG_CONFIG = pg_config
-PGXS := $(shell $(PG_CONFIG) --pgxs)
-include $(PGXS)
-else
-subdir = src/test/modules/test_session_hooks
-top_builddir = ../../../..
-include $(top_builddir)/src/Makefile.global
-include $(top_srcdir)/contrib/contrib-global.mk
-endif
-
-# override installcheck - this module requires preloading the test module
-installcheck:
-	@echo Cannot run $@ for test_session_hooks. Run "'make check'" instead.

src/test/modules/test_session_hooks/README

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

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

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

src/test/modules/test_session_hooks/session_hooks.conf

-shared_preload_libraries = 'test_session_hooks'
-test_session_hooks.username = regress_sess_hook_usr2

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

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

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

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

src/test/modules/test_session_hooks/test_session_hooks.c

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

src/test/modules/test_session_hooks/test_session_hooks.control

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

src/tools/msvc/vcregress.pl

@@ -383,8 +383,6 @@ sub modulescheck
 	my $mstat = 0;
 	foreach my $module (glob("*"))
 	{
-		# test_session_hooks can't run installcheck, so skip it here
-		next if $module eq 'test_session_hooks';
 		subdircheck("$topdir/src/test/modules", $module);
 		my $status = $? >> 8;
 		$mstat ||= $status;