Hi all,

Attached new version of the patch fixing issues about installcheck and some
assertions reported before (based on Michael Paquier code):

https://www.postgresql.org/message-id/flat/30479.1510800078%40sss.pgh.pa.us#30479.1510800...@sss.pgh.pa.us
https://www.postgresql.org/message-id/flat/20171116121823.GI4628%40tamriel.snowman.net#20171116121823.gi4...@tamriel.snowman.net

Regards,

-- 
Fabrízio de Royes Mello
Consultoria/Coaching PostgreSQL
>> Timbira: http://www.timbira.com.br
>> Blog: http://fabriziomello.github.io
>> Linkedin: http://br.linkedin.com/in/fabriziomello
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>> Github: http://github.com/fabriziomello
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 05c5c19..d3156ad 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -169,6 +169,9 @@ 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
  * ----------------------------------------------------------------
@@ -3857,6 +3860,9 @@ PostgresMain(int argc, char *argv[],
 	if (!IsUnderPostmaster)
 		PgStartTime = GetCurrentTimestamp();
 
+	if (session_start_hook)
+		(*session_start_hook) ();
+
 	/*
 	 * POSTGRES main processing loop begins here
 	 *
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index 20f1d27..16ec376 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -76,6 +76,8 @@ 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 ***/
 
@@ -1154,6 +1156,10 @@ ShutdownPostgres(int code, Datum arg)
 	 * them explicitly.
 	 */
 	LockReleaseAll(USER_LOCKMETHOD, true);
+
+	/* Hook at session end */
+	if (session_end_hook)
+		(*session_end_hook) ();
 }
 
 
diff --git a/src/include/tcop/tcopprot.h b/src/include/tcop/tcopprot.h
index f8c535c..9f05bfb 100644
--- a/src/include/tcop/tcopprot.h
+++ b/src/include/tcop/tcopprot.h
@@ -35,6 +35,13 @@ 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
diff --git a/src/test/modules/Makefile b/src/test/modules/Makefile
index b7ed0af..7246552 100644
--- a/src/test/modules/Makefile
+++ b/src/test/modules/Makefile
@@ -15,6 +15,7 @@ SUBDIRS = \
 		  test_pg_dump \
 		  test_rbtree \
 		  test_rls_hooks \
+		  test_session_hooks \
 		  test_shm_mq \
 		  worker_spi
 
diff --git a/src/test/modules/test_session_hooks/.gitignore b/src/test/modules/test_session_hooks/.gitignore
new file mode 100644
index 0000000..5dcb3ff
--- /dev/null
+++ b/src/test/modules/test_session_hooks/.gitignore
@@ -0,0 +1,4 @@
+# Generated subdirectories
+/log/
+/results/
+/tmp_check/
diff --git a/src/test/modules/test_session_hooks/Makefile b/src/test/modules/test_session_hooks/Makefile
new file mode 100644
index 0000000..51683ed
--- /dev/null
+++ b/src/test/modules/test_session_hooks/Makefile
@@ -0,0 +1,46 @@
+# src/test/modules/test_session_hooks/Makefile
+
+MODULES = test_session_hooks
+PGFILEDESC = "test_session_hooks - Test session hooks with an extension"
+
+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
+
+# Disabled because these tests require shared_preload_libraries to be
+# set but users unlikely have that set up.
+installcheck:;
+
+# But it can nonetheless be very helpful to run tests on preexisting
+# installation, allow to do so, but only if requested explicitly.
+installcheck-force: regresscheck-install-force
+
+check: regresscheck
+
+submake-regress:
+	$(MAKE) -C $(top_builddir)/src/test/regress all
+
+submake-test_session_hooks:
+	$(MAKE) -C $(top_builddir)/src/test/modules/test_session_hooks
+
+REGRESSCHECKS = test_session_hooks
+
+regresscheck: | submake-regress submake-test_session_hooks temp-install
+	$(pg_regress_check) $(REGRESS_OPTS) $(REGRESSCHECKS)
+
+regresscheck-install-force: | submake-regress submake-test_session_hooks temp-install
+	$(pg_regress_installcheck) $(REGRESSCHECKS)
+
+.PHONY: submake-test_session_hooks submake-regress check \
+	regresscheck regresscheck-install-force
+
+temp-install: EXTRA_INSTALL=src/test/modules/test_session_hooks
diff --git a/src/test/modules/test_session_hooks/README b/src/test/modules/test_session_hooks/README
new file mode 100644
index 0000000..9cb4202
--- /dev/null
+++ b/src/test/modules/test_session_hooks/README
@@ -0,0 +1,2 @@
+test_session_hooks is an example of how to use session start and end
+hooks.
diff --git a/src/test/modules/test_session_hooks/expected/test_session_hooks.out b/src/test/modules/test_session_hooks/expected/test_session_hooks.out
new file mode 100644
index 0000000..8c1a92f
--- /dev/null
+++ b/src/test/modules/test_session_hooks/expected/test_session_hooks.out
@@ -0,0 +1,33 @@
+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 | 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 | regression | regress_sess_hook_usr2 | START
+  2 | regression | regress_sess_hook_usr2 | END
+(2 rows)
+
+DROP ROLE regress_sess_hook_usr1;
+DROP ROLE regress_sess_hook_usr2;
diff --git a/src/test/modules/test_session_hooks/session_hooks.conf b/src/test/modules/test_session_hooks/session_hooks.conf
new file mode 100644
index 0000000..fc62b4a
--- /dev/null
+++ b/src/test/modules/test_session_hooks/session_hooks.conf
@@ -0,0 +1,2 @@
+shared_preload_libraries = 'test_session_hooks'
+test_session_hooks.username = regress_sess_hook_usr2
diff --git a/src/test/modules/test_session_hooks/sql/test_session_hooks.sql b/src/test/modules/test_session_hooks/sql/test_session_hooks.sql
new file mode 100644
index 0000000..9644c5a
--- /dev/null
+++ b/src/test/modules/test_session_hooks/sql/test_session_hooks.sql
@@ -0,0 +1,14 @@
+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;
+DROP ROLE regress_sess_hook_usr1;
+DROP ROLE regress_sess_hook_usr2;
diff --git a/src/test/modules/test_session_hooks/test_session_hooks.c b/src/test/modules/test_session_hooks/test_session_hooks.c
new file mode 100644
index 0000000..3dc93b7
--- /dev/null
+++ b/src/test/modules/test_session_hooks/test_session_hooks.c
@@ -0,0 +1,143 @@
+/* -------------------------------------------------------------------------
+ *
+ * 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 "postmaster/autovacuum.h"
+#include "replication/walsender.h"
+#include "tcop/tcopprot.h"
+#include "utils/builtins.h"
+#include "utils/snapmgr.h"
+
+#define IsClientBackend() \
+	(MyBackendId != InvalidBackendId &&	\
+	 !IsAutoVacuumLauncherProcess() &&	\
+	 !IsAutoVacuumWorkerProcess() && \
+	 !am_walsender && \
+	 !IsBackgroundWorker)
+
+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(void)
+{
+	/* Hook just client backends */
+	if (IsClientBackend())
+	{
+		(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(void)
+{
+	/* Hook just client backends */
+	if (IsClientBackend())
+	{
+		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;
+}

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