Add support event triggers on authenticated login

This commit introduces trigger on login event, allowing to fire some actions
right on the user connection.  This can be useful for logging or connection
check purposes as well as for some personalization of environment.  Usage
details are described in the documentation included, but shortly usage is
the same as for other triggers: create function returning event_trigger and
then create event trigger on login event.

In order to prevent the connection time overhead when there are no triggers
the commit introduces pg_database.dathasloginevt flag, which indicates database
has active login triggers.  This flag is set by CREATE/ALTER EVENT TRIGGER
command, and unset at connection time when no active triggers found.

Author: Konstantin Knizhnik, Mikhail Gribkov
Discussion: https://postgr.es/m/0d46d29f-4558-3af9-9c85-7774e14a7709%40postgrespro.ru
Reviewed-by: Pavel Stehule, Takayuki Tsunakawa, Greg Nancarrow, Ivan Panchenko
Reviewed-by: Daniel Gustafsson, Teodor Sigaev, Robert Haas, Andres Freund
Reviewed-by: Tom Lane, Andrey Sokolov, Zhihong Yu, Sergey Shinderuk
Reviewed-by: Gregory Stark, Nikita Malakhov, Ted Yu

1 files changed, 11 insertions, 6 deletions

diff --git a/src/backend/commands/dbcommands.c b/src/backend/commands/dbcommands.c
index 307729ab7ef..c52ecc61a6b 100644
--- a/src/backend/commands/dbcommands.c
+++ b/src/backend/commands/dbcommands.c
@@ -116,7 +116,7 @@ static void movedb(const char *dbname, const char *tblspcname);
 static void movedb_failure_callback(int code, Datum arg);
 static bool get_db_info(const char *name, LOCKMODE lockmode,
 						Oid *dbIdP, Oid *ownerIdP,
-						int *encodingP, bool *dbIsTemplateP, bool *dbAllowConnP,
+						int *encodingP, bool *dbIsTemplateP, bool *dbAllowConnP, bool *dbHasLoginEvtP,
 						TransactionId *dbFrozenXidP, MultiXactId *dbMinMultiP,
 						Oid *dbTablespace, char **dbCollate, char **dbCtype, char **dbIculocale,
 						char **dbIcurules,
@@ -680,6 +680,7 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	char		src_locprovider = '\0';
 	char	   *src_collversion = NULL;
 	bool		src_istemplate;
+	bool		src_hasloginevt;
 	bool		src_allowconn;
 	TransactionId src_frozenxid = InvalidTransactionId;
 	MultiXactId src_minmxid = InvalidMultiXactId;
@@ -968,7 +969,7 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 
 	if (!get_db_info(dbtemplate, ShareLock,
 					 &src_dboid, &src_owner, &src_encoding,
-					 &src_istemplate, &src_allowconn,
+					 &src_istemplate, &src_allowconn, &src_hasloginevt,
 					 &src_frozenxid, &src_minmxid, &src_deftablespace,
 					 &src_collate, &src_ctype, &src_iculocale, &src_icurules, &src_locprovider,
 					 &src_collversion))
@@ -1375,6 +1376,7 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	new_record[Anum_pg_database_datlocprovider - 1] = CharGetDatum(dblocprovider);
 	new_record[Anum_pg_database_datistemplate - 1] = BoolGetDatum(dbistemplate);
 	new_record[Anum_pg_database_datallowconn - 1] = BoolGetDatum(dballowconnections);
+	new_record[Anum_pg_database_dathasloginevt - 1] = BoolGetDatum(src_hasloginevt);
 	new_record[Anum_pg_database_datconnlimit - 1] = Int32GetDatum(dbconnlimit);
 	new_record[Anum_pg_database_datfrozenxid - 1] = TransactionIdGetDatum(src_frozenxid);
 	new_record[Anum_pg_database_datminmxid - 1] = TransactionIdGetDatum(src_minmxid);
@@ -1603,7 +1605,7 @@ dropdb(const char *dbname, bool missing_ok, bool force)
 	pgdbrel = table_open(DatabaseRelationId, RowExclusiveLock);
 
 	if (!get_db_info(dbname, AccessExclusiveLock, &db_id, NULL, NULL,
-					 &db_istemplate, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
+					 &db_istemplate, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
 	{
 		if (!missing_ok)
 		{
@@ -1817,7 +1819,7 @@ RenameDatabase(const char *oldname, const char *newname)
 	 */
 	rel = table_open(DatabaseRelationId, RowExclusiveLock);
 
-	if (!get_db_info(oldname, AccessExclusiveLock, &db_id, NULL, NULL,
+	if (!get_db_info(oldname, AccessExclusiveLock, &db_id, NULL, NULL, NULL,
 					 NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_DATABASE),
@@ -1927,7 +1929,7 @@ movedb(const char *dbname, const char *tblspcname)
 	 */
 	pgdbrel = table_open(DatabaseRelationId, RowExclusiveLock);
 
-	if (!get_db_info(dbname, AccessExclusiveLock, &db_id, NULL, NULL,
+	if (!get_db_info(dbname, AccessExclusiveLock, &db_id, NULL, NULL, NULL,
 					 NULL, NULL, NULL, NULL, &src_tblspcoid, NULL, NULL, NULL, NULL, NULL, NULL))
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_DATABASE),
@@ -2693,7 +2695,7 @@ pg_database_collation_actual_version(PG_FUNCTION_ARGS)
 static bool
 get_db_info(const char *name, LOCKMODE lockmode,
 			Oid *dbIdP, Oid *ownerIdP,
-			int *encodingP, bool *dbIsTemplateP, bool *dbAllowConnP,
+			int *encodingP, bool *dbIsTemplateP, bool *dbAllowConnP, bool *dbHasLoginEvtP,
 			TransactionId *dbFrozenXidP, MultiXactId *dbMinMultiP,
 			Oid *dbTablespace, char **dbCollate, char **dbCtype, char **dbIculocale,
 			char **dbIcurules,
@@ -2778,6 +2780,9 @@ get_db_info(const char *name, LOCKMODE lockmode,
 				/* allowed as template? */
 				if (dbIsTemplateP)
 					*dbIsTemplateP = dbform->datistemplate;
+				/* Has on login event trigger? */
+				if (dbHasLoginEvtP)
+					*dbHasLoginEvtP = dbform->dathasloginevt;
 				/* allowing connections? */
 				if (dbAllowConnP)
 					*dbAllowConnP = dbform->datallowconn;