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

21 files changed, 534 insertions, 20 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;
diff --git a/src/backend/commands/event_trigger.c b/src/backend/commands/event_trigger.c
index bd812e42d94..0b08552fd7a 100644
--- a/src/backend/commands/event_trigger.c
+++ b/src/backend/commands/event_trigger.c
@@ -20,6 +20,7 @@
 #include "catalog/dependency.h"
 #include "catalog/indexing.h"
 #include "catalog/objectaccess.h"
+#include "catalog/pg_database.h"
 #include "catalog/pg_event_trigger.h"
 #include "catalog/pg_namespace.h"
 #include "catalog/pg_opclass.h"
@@ -37,15 +38,18 @@
 #include "miscadmin.h"
 #include "parser/parse_func.h"
 #include "pgstat.h"
+#include "storage/lmgr.h"
 #include "tcop/deparse_utility.h"
 #include "tcop/utility.h"
 #include "utils/acl.h"
 #include "utils/builtins.h"
 #include "utils/evtcache.h"
 #include "utils/fmgroids.h"
+#include "utils/inval.h"
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
 #include "utils/rel.h"
+#include "utils/snapmgr.h"
 #include "utils/syscache.h"
 
 typedef struct EventTriggerQueryState
@@ -103,6 +107,7 @@ static void validate_table_rewrite_tags(const char *filtervar, List *taglist);
 static void EventTriggerInvoke(List *fn_oid_list, EventTriggerData *trigdata);
 static const char *stringify_grant_objtype(ObjectType objtype);
 static const char *stringify_adefprivs_objtype(ObjectType objtype);
+static void SetDatatabaseHasLoginEventTriggers(void);
 
 /*
  * Create an event trigger.
@@ -133,6 +138,7 @@ CreateEventTrigger(CreateEventTrigStmt *stmt)
 	if (strcmp(stmt->eventname, "ddl_command_start") != 0 &&
 		strcmp(stmt->eventname, "ddl_command_end") != 0 &&
 		strcmp(stmt->eventname, "sql_drop") != 0 &&
+		strcmp(stmt->eventname, "login") != 0 &&
 		strcmp(stmt->eventname, "table_rewrite") != 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_SYNTAX_ERROR),
@@ -165,6 +171,10 @@ CreateEventTrigger(CreateEventTrigStmt *stmt)
 	else if (strcmp(stmt->eventname, "table_rewrite") == 0
 			 && tags != NULL)
 		validate_table_rewrite_tags("tag", tags);
+	else if (strcmp(stmt->eventname, "login") == 0 && tags != NULL)
+			ereport(ERROR,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					 errmsg("Tag filtering is not supported for login event trigger")));
 
 	/*
 	 * Give user a nice error message if an event trigger of the same name
@@ -296,6 +306,13 @@ insert_event_trigger_tuple(const char *trigname, const char *eventname, Oid evtO
 	CatalogTupleInsert(tgrel, tuple);
 	heap_freetuple(tuple);
 
+	/*
+	 * Login event triggers have an additional flag in pg_database to avoid
+	 * faster lookups in hot codepaths. Set the flag unless already True.
+	 */
+	if (strcmp(eventname, "login") == 0)
+		SetDatatabaseHasLoginEventTriggers();
+
 	/* Depend on owner. */
 	recordDependencyOnOwner(EventTriggerRelationId, trigoid, evtOwner);
 
@@ -358,6 +375,41 @@ filter_list_to_array(List *filterlist)
 }
 
 /*
+ * Set pg_database.dathasloginevt flag for current database indicating that
+ * current database has on login triggers.
+ */
+void
+SetDatatabaseHasLoginEventTriggers(void)
+{
+	/* Set dathasloginevt flag in pg_database */
+	Form_pg_database db;
+	Relation	pg_db = table_open(DatabaseRelationId, RowExclusiveLock);
+	HeapTuple	tuple;
+
+	/*
+	 * Use shared lock to prevent a conflit with EventTriggerOnLogin() trying
+	 * to reset pg_database.dathasloginevt flag.  Note, this lock doesn't
+	 * effectively blocks database or other objection.  It's just custom lock
+	 * tag used to prevent multiple backends changing pg_database.dathasloginevt
+	 * flag.
+	 */
+	LockSharedObject(DatabaseRelationId, MyDatabaseId, 0, AccessExclusiveLock);
+
+	tuple = SearchSysCacheCopy1(DATABASEOID, ObjectIdGetDatum(MyDatabaseId));
+	if (!HeapTupleIsValid(tuple))
+		elog(ERROR, "cache lookup failed for database %u", MyDatabaseId);
+	db = (Form_pg_database) GETSTRUCT(tuple);
+	if (!db->dathasloginevt)
+	{
+		db->dathasloginevt = true;
+		CatalogTupleUpdate(pg_db, &tuple->t_self, tuple);
+		CommandCounterIncrement();
+	}
+	table_close(pg_db, RowExclusiveLock);
+	heap_freetuple(tuple);
+}
+
+/*
  * ALTER EVENT TRIGGER foo ENABLE|DISABLE|ENABLE ALWAYS|REPLICA
  */
 Oid
@@ -391,6 +443,14 @@ AlterEventTrigger(AlterEventTrigStmt *stmt)
 
 	CatalogTupleUpdate(tgrel, &tup->t_self, tup);
 
+	/*
+	 * Login event triggers have an additional flag in pg_database to avoid
+	 * faster lookups in hot codepaths. Set the flag unless already True.
+	 */
+	if (namestrcmp(&evtForm->evtevent, "login") == 0 &&
+		tgenabled != TRIGGER_DISABLED)
+		SetDatatabaseHasLoginEventTriggers();
+
 	InvokeObjectPostAlterHook(EventTriggerRelationId,
 							  trigoid, 0);
 
@@ -549,6 +609,15 @@ filter_event_trigger(CommandTag tag, EventTriggerCacheItem *item)
 	return true;
 }
 
+static CommandTag
+EventTriggerGetTag(Node *parsetree, EventTriggerEvent event)
+{
+	if (event == EVT_Login)
+		return CMDTAG_LOGIN;
+	else
+		return CreateCommandTag(parsetree);
+}
+
 /*
  * Setup for running triggers for the given event.  Return value is an OID list
  * of functions to run; if there are any, trigdata is filled with an
@@ -557,7 +626,7 @@ filter_event_trigger(CommandTag tag, EventTriggerCacheItem *item)
 static List *
 EventTriggerCommonSetup(Node *parsetree,
 						EventTriggerEvent event, const char *eventstr,
-						EventTriggerData *trigdata)
+						EventTriggerData *trigdata, bool unfiltered)
 {
 	CommandTag	tag;
 	List	   *cachelist;
@@ -582,10 +651,12 @@ EventTriggerCommonSetup(Node *parsetree,
 	{
 		CommandTag	dbgtag;
 
-		dbgtag = CreateCommandTag(parsetree);
+		dbgtag = EventTriggerGetTag(parsetree, event);
+
 		if (event == EVT_DDLCommandStart ||
 			event == EVT_DDLCommandEnd ||
-			event == EVT_SQLDrop)
+			event == EVT_SQLDrop ||
+			event == EVT_Login)
 		{
 			if (!command_tag_event_trigger_ok(dbgtag))
 				elog(ERROR, "unexpected command tag \"%s\"", GetCommandTagName(dbgtag));
@@ -604,7 +675,7 @@ EventTriggerCommonSetup(Node *parsetree,
 		return NIL;
 
 	/* Get the command tag. */
-	tag = CreateCommandTag(parsetree);
+	tag = EventTriggerGetTag(parsetree, event);
 
 	/*
 	 * Filter list of event triggers by command tag, and copy them into our
@@ -617,7 +688,7 @@ EventTriggerCommonSetup(Node *parsetree,
 	{
 		EventTriggerCacheItem *item = lfirst(lc);
 
-		if (filter_event_trigger(tag, item))
+		if (unfiltered || filter_event_trigger(tag, item))
 		{
 			/* We must plan to fire this trigger. */
 			runlist = lappend_oid(runlist, item->fnoid);
@@ -670,7 +741,7 @@ EventTriggerDDLCommandStart(Node *parsetree)
 	runlist = EventTriggerCommonSetup(parsetree,
 									  EVT_DDLCommandStart,
 									  "ddl_command_start",
-									  &trigdata);
+									  &trigdata, false);
 	if (runlist == NIL)
 		return;
 
@@ -718,7 +789,7 @@ EventTriggerDDLCommandEnd(Node *parsetree)
 
 	runlist = EventTriggerCommonSetup(parsetree,
 									  EVT_DDLCommandEnd, "ddl_command_end",
-									  &trigdata);
+									  &trigdata, false);
 	if (runlist == NIL)
 		return;
 
@@ -764,7 +835,7 @@ EventTriggerSQLDrop(Node *parsetree)
 
 	runlist = EventTriggerCommonSetup(parsetree,
 									  EVT_SQLDrop, "sql_drop",
-									  &trigdata);
+									  &trigdata, false);
 
 	/*
 	 * Nothing to do if run list is empty.  Note this typically can't happen,
@@ -805,6 +876,96 @@ EventTriggerSQLDrop(Node *parsetree)
 	list_free(runlist);
 }
 
+/*
+ * Fire login event triggers if any are present.  The dathasloginevt
+ * pg_database flag is left when an event trigger is dropped, to avoid
+ * complicating the codepath in the case of multiple event triggers.  This
+ * function will instead unset the flag if no trigger is defined.
+ */
+void
+EventTriggerOnLogin(void)
+{
+	List	   *runlist;
+	EventTriggerData trigdata;
+
+	/*
+	 * See EventTriggerDDLCommandStart for a discussion about why event
+	 * triggers are disabled in single user mode or via a GUC.  We also need a
+	 * database connection (some background workers doesn't have it).
+	 */
+	if (!IsUnderPostmaster || !event_triggers ||
+		!OidIsValid(MyDatabaseId) || !MyDatabaseHasLoginEventTriggers)
+		return;
+
+	StartTransactionCommand();
+	runlist = EventTriggerCommonSetup(NULL,
+										EVT_Login, "login",
+										&trigdata, false);
+
+	if (runlist != NIL)
+	{
+		/*
+		 * Event trigger execution may require an active snapshot.
+		 */
+		PushActiveSnapshot(GetTransactionSnapshot());
+
+		/* Run the triggers. */
+		EventTriggerInvoke(runlist, &trigdata);
+
+		/* Cleanup. */
+		list_free(runlist);
+
+		PopActiveSnapshot();
+	}
+	/*
+	 * There is no active login event trigger, but our pg_database.dathasloginevt was set.
+	 * Try to unset this flag.  We use the lock to prevent concurrent
+	 * SetDatatabaseHasLoginEventTriggers(), but we don't want to hang the
+	 * connection waiting on the lock.  Thus, we are just trying to acquire
+	 * the lock conditionally.
+	 */
+	else if (ConditionalLockSharedObject(DatabaseRelationId, MyDatabaseId,
+										 0, AccessExclusiveLock))
+	{
+		/*
+		 * The lock is held.  Now we need to recheck that login event triggers
+		 * list is still empty.  Once the list is empty, we know that even if
+		 * there is a backend, which concurrently inserts/enables login trigger,
+		 * it will update pg_database.dathasloginevt *afterwards*.
+		 */
+		runlist = EventTriggerCommonSetup(NULL,
+										  EVT_Login, "login",
+										  &trigdata, true);
+
+		if (runlist == NIL)
+		{
+			Relation	pg_db = table_open(DatabaseRelationId, RowExclusiveLock);
+			HeapTuple	tuple;
+			Form_pg_database db;
+
+			tuple = SearchSysCacheCopy1(DATABASEOID,
+										ObjectIdGetDatum(MyDatabaseId));
+
+			if (!HeapTupleIsValid(tuple))
+				elog(ERROR, "cache lookup failed for database %u", MyDatabaseId);
+
+			db = (Form_pg_database) GETSTRUCT(tuple);
+			if (db->dathasloginevt)
+			{
+				db->dathasloginevt = false;
+				CatalogTupleUpdate(pg_db, &tuple->t_self, tuple);
+			}
+			table_close(pg_db, RowExclusiveLock);
+			heap_freetuple(tuple);
+		}
+		else
+		{
+			list_free(runlist);
+		}
+	}
+	CommitTransactionCommand();
+}
+
 
 /*
  * Fire table_rewrite triggers.
@@ -835,7 +996,7 @@ EventTriggerTableRewrite(Node *parsetree, Oid tableOid, int reason)
 	runlist = EventTriggerCommonSetup(parsetree,
 									  EVT_TableRewrite,
 									  "table_rewrite",
-									  &trigdata);
+									  &trigdata, false);
 	if (runlist == NIL)
 		return;
 
diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c
index ee9b89a6726..b447ddf11ba 100644
--- a/src/backend/storage/lmgr/lmgr.c
+++ b/src/backend/storage/lmgr/lmgr.c
@@ -1061,6 +1061,44 @@ LockSharedObject(Oid classid, Oid objid, uint16 objsubid,
 }
 
 /*
+ *		ConditionalLockSharedObject
+ *
+ * As above, but only lock if we can get the lock without blocking.
+ * Returns true iff the lock was acquired.
+ */
+bool
+ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid,
+							LOCKMODE lockmode)
+{
+	LOCKTAG		tag;
+	LOCALLOCK  *locallock;
+	LockAcquireResult res;
+
+	SET_LOCKTAG_OBJECT(tag,
+					   InvalidOid,
+					   classid,
+					   objid,
+					   objsubid);
+
+	res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock);
+
+	if (res == LOCKACQUIRE_NOT_AVAIL)
+		return false;
+
+	/*
+	 * Now that we have the lock, check for invalidation messages; see notes
+	 * in LockRelationOid.
+	 */
+	if (res != LOCKACQUIRE_ALREADY_CLEAR)
+	{
+		AcceptInvalidationMessages();
+		MarkLockClear(locallock);
+	}
+
+	return true;
+}
+
+/*
  *		UnlockSharedObject
  */
 void
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index f3c9f1f9bab..c900427ecf9 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -36,6 +36,7 @@
 #include "access/xact.h"
 #include "catalog/pg_type.h"
 #include "commands/async.h"
+#include "commands/event_trigger.h"
 #include "commands/prepare.h"
 #include "common/pg_prng.h"
 #include "jit/jit.h"
@@ -4289,6 +4290,9 @@ PostgresMain(const char *dbname, const char *username)
 	initStringInfo(&row_description_buf);
 	MemoryContextSwitchTo(TopMemoryContext);
 
+	/* Fire any defined login event triggers, if appropriate */
+	EventTriggerOnLogin();
+
 	/*
 	 * POSTGRES main processing loop begins here
 	 *
diff --git a/src/backend/utils/cache/evtcache.c b/src/backend/utils/cache/evtcache.c
index b080f7a35f3..ab5111c90fd 100644
--- a/src/backend/utils/cache/evtcache.c
+++ b/src/backend/utils/cache/evtcache.c
@@ -167,6 +167,8 @@ BuildEventTriggerCache(void)
 			event = EVT_SQLDrop;
 		else if (strcmp(evtevent, "table_rewrite") == 0)
 			event = EVT_TableRewrite;
+		else if (strcmp(evtevent, "login") == 0)
+			event = EVT_Login;
 		else
 			continue;
 
diff --git a/src/backend/utils/init/globals.c b/src/backend/utils/init/globals.c
index 011ec18015a..60bc1217fb4 100644
--- a/src/backend/utils/init/globals.c
+++ b/src/backend/utils/init/globals.c
@@ -90,6 +90,8 @@ Oid			MyDatabaseId = InvalidOid;
 
 Oid			MyDatabaseTableSpace = InvalidOid;
 
+bool		MyDatabaseHasLoginEventTriggers = false;
+
 /*
  * DatabasePath is the path (relative to DataDir) of my database's
  * primary directory, ie, its directory in the default tablespace.
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index e60ecd1e366..552cf9d950a 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -1103,6 +1103,7 @@ InitPostgres(const char *in_dbname, Oid dboid,
 		}
 
 		MyDatabaseTableSpace = datform->dattablespace;
+		MyDatabaseHasLoginEventTriggers = datform->dathasloginevt;
 		/* pass the database name back to the caller */
 		if (out_dbname)
 			strcpy(out_dbname, dbname);
diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index f7b61766921..83aeef2751b 100644
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -3263,6 +3263,11 @@ dumpDatabase(Archive *fout)
 		appendPQExpBufferStr(delQry, ";\n");
 	}
 
+	/*
+	 * We do not restore pg_database.dathasloginevt because it is set
+	 * automatically on login event trigger creation.
+	 */
+
 	/* Add database-specific SET options */
 	dumpDatabaseConfig(fout, creaQry, datname, dbCatId.oid);
 
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index eb4dfe80b50..93742fc6ac9 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -3552,8 +3552,8 @@ psql_completion(const char *text, int start, int end)
 		COMPLETE_WITH("ON");
 	/* Complete CREATE EVENT TRIGGER <name> ON with event_type */
 	else if (Matches("CREATE", "EVENT", "TRIGGER", MatchAny, "ON"))
-		COMPLETE_WITH("ddl_command_start", "ddl_command_end", "sql_drop",
-					  "table_rewrite");
+		COMPLETE_WITH("ddl_command_start", "ddl_command_end", "login",
+					  "sql_drop", "table_rewrite");
 
 	/*
 	 * Complete CREATE EVENT TRIGGER <name> ON <event_type>.  EXECUTE FUNCTION
diff --git a/src/include/catalog/catversion.h b/src/include/catalog/catversion.h
index 5efc1445207..c5f4af24dc1 100644
--- a/src/include/catalog/catversion.h
+++ b/src/include/catalog/catversion.h
@@ -57,6 +57,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	202310141
+#define CATALOG_VERSION_NO	202310161
 
 #endif
diff --git a/src/include/catalog/pg_database.dat b/src/include/catalog/pg_database.dat
index 0754ef1bce4..8d91e3bf8da 100644
--- a/src/include/catalog/pg_database.dat
+++ b/src/include/catalog/pg_database.dat
@@ -16,7 +16,7 @@
   descr => 'default template for new databases',
   datname => 'template1', encoding => 'ENCODING',
   datlocprovider => 'LOCALE_PROVIDER', datistemplate => 't',
-  datallowconn => 't', datconnlimit => '-1', datfrozenxid => '0',
+  datallowconn => 't', dathasloginevt => 'f', datconnlimit => '-1', datfrozenxid => '0',
   datminmxid => '1', dattablespace => 'pg_default', datcollate => 'LC_COLLATE',
   datctype => 'LC_CTYPE', daticulocale => 'ICU_LOCALE',
   daticurules => 'ICU_RULES', datacl => '_null_' },
diff --git a/src/include/catalog/pg_database.h b/src/include/catalog/pg_database.h
index e9eb06b2e53..3e50a570046 100644
--- a/src/include/catalog/pg_database.h
+++ b/src/include/catalog/pg_database.h
@@ -49,6 +49,9 @@ CATALOG(pg_database,1262,DatabaseRelationId) BKI_SHARED_RELATION BKI_ROWTYPE_OID
 	/* new connections allowed? */
 	bool		datallowconn;
 
+	/* database has login event triggers? */
+	bool		dathasloginevt;
+
 	/*
 	 * Max connections allowed. Negative values have special meaning, see
 	 * DATCONNLIMIT_* defines below.
diff --git a/src/include/commands/event_trigger.h b/src/include/commands/event_trigger.h
index 1c925dbf257..9e3ece50d5f 100644
--- a/src/include/commands/event_trigger.h
+++ b/src/include/commands/event_trigger.h
@@ -56,6 +56,7 @@ extern void EventTriggerDDLCommandStart(Node *parsetree);
 extern void EventTriggerDDLCommandEnd(Node *parsetree);
 extern void EventTriggerSQLDrop(Node *parsetree);
 extern void EventTriggerTableRewrite(Node *parsetree, Oid tableOid, int reason);
+extern void EventTriggerOnLogin(void);
 
 extern bool EventTriggerBeginCompleteQuery(void);
 extern void EventTriggerEndCompleteQuery(void);
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index c2f9de63a13..7232b03e379 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -203,6 +203,8 @@ extern PGDLLIMPORT Oid MyDatabaseId;
 
 extern PGDLLIMPORT Oid MyDatabaseTableSpace;
 
+extern PGDLLIMPORT bool MyDatabaseHasLoginEventTriggers;
+
 /*
  * Date/Time Configuration
  *
diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h
index 4ee91e3cf93..952ebe75cb4 100644
--- a/src/include/storage/lmgr.h
+++ b/src/include/storage/lmgr.h
@@ -99,6 +99,8 @@ extern void UnlockDatabaseObject(Oid classid, Oid objid, uint16 objsubid,
 /* Lock a shared-across-databases object (other than a relation) */
 extern void LockSharedObject(Oid classid, Oid objid, uint16 objsubid,
 							 LOCKMODE lockmode);
+extern bool ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid,
+										LOCKMODE lockmode);
 extern void UnlockSharedObject(Oid classid, Oid objid, uint16 objsubid,
 							   LOCKMODE lockmode);
 
diff --git a/src/include/tcop/cmdtaglist.h b/src/include/tcop/cmdtaglist.h
index e738ac1c097..553a31874f1 100644
--- a/src/include/tcop/cmdtaglist.h
+++ b/src/include/tcop/cmdtaglist.h
@@ -186,6 +186,7 @@ PG_CMDTAG(CMDTAG_INSERT, "INSERT", false, false, true)
 PG_CMDTAG(CMDTAG_LISTEN, "LISTEN", false, false, false)
 PG_CMDTAG(CMDTAG_LOAD, "LOAD", false, false, false)
 PG_CMDTAG(CMDTAG_LOCK_TABLE, "LOCK TABLE", false, false, false)
+PG_CMDTAG(CMDTAG_LOGIN, "LOGIN", true, false, false)
 PG_CMDTAG(CMDTAG_MERGE, "MERGE", false, false, true)
 PG_CMDTAG(CMDTAG_MOVE, "MOVE", false, false, true)
 PG_CMDTAG(CMDTAG_NOTIFY, "NOTIFY", false, false, false)
diff --git a/src/include/utils/evtcache.h b/src/include/utils/evtcache.h
index d340026518a..52052e6252a 100644
--- a/src/include/utils/evtcache.h
+++ b/src/include/utils/evtcache.h
@@ -22,7 +22,8 @@ typedef enum
 	EVT_DDLCommandStart,
 	EVT_DDLCommandEnd,
 	EVT_SQLDrop,
-	EVT_TableRewrite
+	EVT_TableRewrite,
+	EVT_Login,
 } EventTriggerEvent;
 
 typedef struct
diff --git a/src/test/authentication/t/005_login_trigger.pl b/src/test/authentication/t/005_login_trigger.pl
new file mode 100644
index 00000000000..f317012a19d
--- /dev/null
+++ b/src/test/authentication/t/005_login_trigger.pl
@@ -0,0 +1,189 @@
+# Copyright (c) 2021-2023, PostgreSQL Global Development Group
+
+# Tests of authentication via login trigger. Mostly for rejection via
+# exception, because this scenario cannot be covered with *.sql/*.out regress
+# tests.
+
+use strict;
+use warnings;
+
+use PostgreSQL::Test::Cluster;
+use PostgreSQL::Test::Utils;
+use Test::More;
+
+# Execute a psql command and compare its output towards given regexps
+sub psql_command
+{
+	local $Test::Builder::Level = $Test::Builder::Level + 1;
+	my ($node, $sql, $expected_ret, $test_name, %params) = @_;
+
+	my $connstr;
+	if (defined($params{connstr}))
+	{
+		$connstr = $params{connstr};
+	}
+	else
+	{
+		$connstr = '';
+	}
+
+	# Execute command
+	my ($ret, $stdout, $stderr) =
+	  $node->psql('postgres', $sql, connstr => "$connstr");
+
+	# Check return code
+	is($ret, $expected_ret, "$test_name: exit code $expected_ret");
+
+	# Check stdout
+	if (defined($params{log_like}))
+	{
+		my @log_like = @{ $params{log_like} };
+		while (my $regex = shift @log_like)
+		{
+			like($stdout, $regex, "$test_name: log matches");
+		}
+	}
+	if (defined($params{log_unlike}))
+	{
+		my @log_unlike = @{ $params{log_unlike} };
+		while (my $regex = shift @log_unlike)
+		{
+			unlike($stdout, $regex, "$test_name: log unmatches");
+		}
+	}
+	if (defined($params{log_exact}))
+	{
+		is($stdout, $params{log_exact}, "$test_name: log equals");
+	}
+
+	# Check stderr
+	if (defined($params{err_like}))
+	{
+		my @err_like = @{ $params{err_like} };
+		while (my $regex = shift @err_like)
+		{
+			like($stderr, $regex, "$test_name: err matches");
+		}
+	}
+	if (defined($params{err_unlike}))
+	{
+		my @err_unlike = @{ $params{err_unlike} };
+		while (my $regex = shift @err_unlike)
+		{
+			unlike($stderr, $regex, "$test_name: err unmatches");
+		}
+	}
+	if (defined($params{err_exact}))
+	{
+		is($stderr, $params{err_exact}, "$test_name: err equals");
+	}
+
+	return;
+}
+
+# New node
+my $node = PostgreSQL::Test::Cluster->new('main');
+$node->init(extra => [ '--locale=C', '--encoding=UTF8' ]);
+$node->append_conf(
+	'postgresql.conf', q{
+wal_level = 'logical'
+max_replication_slots = 4
+max_wal_senders = 4
+});
+$node->start;
+
+# Create temporary roles and log table
+psql_command(
+	$node, 'CREATE ROLE alice WITH LOGIN;
+CREATE ROLE mallory WITH LOGIN;
+CREATE TABLE user_logins(id serial, who text);
+GRANT SELECT ON user_logins TO public;
+', 0, 'create tmp objects',
+	log_exact => '',
+	err_exact => ''),
+  ;
+
+# Create login event function and trigger
+psql_command(
+	$node,
+	'CREATE FUNCTION on_login_proc() RETURNS event_trigger AS $$
+BEGIN
+  INSERT INTO user_logins (who) VALUES (SESSION_USER);
+  IF SESSION_USER = \'mallory\' THEN
+    RAISE EXCEPTION \'Hello %! You are NOT welcome here!\', SESSION_USER;
+  END IF;
+  RAISE NOTICE \'Hello %! You are welcome!\', SESSION_USER;
+END;
+$$ LANGUAGE plpgsql SECURITY DEFINER;
+', 0, 'create trigger function',
+	log_exact => '',
+	err_exact => '');
+
+psql_command(
+	$node,
+	'CREATE EVENT TRIGGER on_login_trigger '
+	  . 'ON login EXECUTE PROCEDURE on_login_proc();', 0,
+	'create event trigger',
+	log_exact => '',
+	err_exact => '');
+psql_command(
+	$node, 'ALTER EVENT TRIGGER on_login_trigger ENABLE ALWAYS;', 0,
+	'alter event trigger',
+	log_exact => '',
+	err_like => [qr/You are welcome/]);
+
+# Check the two requests were logged via login trigger
+psql_command(
+	$node, 'SELECT COUNT(*) FROM user_logins;', 0, 'select count',
+	log_exact => '2',
+	err_like => [qr/You are welcome/]);
+
+# Try to log as allowed Alice and disallowed Mallory (two times)
+psql_command(
+	$node, 'SELECT 1;', 0, 'try alice',
+	connstr => 'user=alice',
+	log_exact => '1',
+	err_like => [qr/You are welcome/],
+	err_unlike => [qr/You are NOT welcome/]);
+psql_command(
+	$node, 'SELECT 1;', 2, 'try mallory',
+	connstr => 'user=mallory',
+	log_exact => '',
+	err_like => [qr/You are NOT welcome/],
+	err_unlike => [qr/You are welcome/]);
+psql_command(
+	$node, 'SELECT 1;', 2, 'try mallory',
+	connstr => 'user=mallory',
+	log_exact => '',
+	err_like => [qr/You are NOT welcome/],
+	err_unlike => [qr/You are welcome/]);
+
+# Check that Alice's login record is here, while the Mallory's one is not
+psql_command(
+	$node, 'SELECT * FROM user_logins;', 0, 'select *',
+	log_like => [qr/3\|alice/],
+	log_unlike => [qr/mallory/],
+	err_like => [qr/You are welcome/]);
+
+# Check total number of successful logins so far
+psql_command(
+	$node, 'SELECT COUNT(*) FROM user_logins;', 0, 'select count',
+	log_exact => '5',
+	err_like => [qr/You are welcome/]);
+
+# Cleanup the temporary stuff
+psql_command(
+	$node, 'DROP EVENT TRIGGER on_login_trigger;', 0,
+	'drop event trigger',
+	log_exact => '',
+	err_like => [qr/You are welcome/]);
+psql_command(
+	$node, 'DROP TABLE user_logins;
+DROP FUNCTION on_login_proc;
+DROP ROLE mallory;
+DROP ROLE alice;
+', 0, 'cleanup',
+	log_exact => '',
+	err_exact => '');
+
+done_testing();
diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index 0c72ba09441..95f9b0d7726 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -46,6 +46,25 @@ $node_standby_2->start;
 $node_primary->safe_psql('postgres',
 	"CREATE TABLE tab_int AS SELECT generate_series(1,1002) AS a");
 
+$node_primary->safe_psql(
+	'postgres', q{
+CREATE TABLE user_logins(id serial, who text);
+
+CREATE FUNCTION on_login_proc() RETURNS EVENT_TRIGGER AS $$
+BEGIN
+  IF NOT pg_is_in_recovery() THEN
+    INSERT INTO user_logins (who) VALUES (session_user);
+  END IF;
+  IF session_user = 'regress_hacker' THEN
+    RAISE EXCEPTION 'You are not welcome!';
+  END IF;
+END;
+$$ LANGUAGE plpgsql SECURITY DEFINER;
+
+CREATE EVENT TRIGGER on_login_trigger ON login EXECUTE FUNCTION on_login_proc();
+ALTER EVENT TRIGGER on_login_trigger ENABLE ALWAYS;
+});
+
 # Wait for standbys to catch up
 $node_primary->wait_for_replay_catchup($node_standby_1);
 $node_standby_1->wait_for_replay_catchup($node_standby_2, $node_primary);
@@ -384,6 +403,13 @@ sub replay_check
 
 replay_check();
 
+my $evttrig = $node_standby_1->safe_psql('postgres',
+	"SELECT evtname FROM pg_event_trigger WHERE evtevent = 'login'");
+is($evttrig, 'on_login_trigger', 'Name of login trigger');
+$evttrig = $node_standby_2->safe_psql('postgres',
+	"SELECT evtname FROM pg_event_trigger WHERE evtevent = 'login'");
+is($evttrig, 'on_login_trigger', 'Name of login trigger');
+
 note "enabling hot_standby_feedback";
 
 # Enable hs_feedback. The slot should gain an xmin. We set the status interval
diff --git a/src/test/regress/expected/event_trigger.out b/src/test/regress/expected/event_trigger.out
index 0b87a42d0a9..eaaff6ba6f1 100644
--- a/src/test/regress/expected/event_trigger.out
+++ b/src/test/regress/expected/event_trigger.out
@@ -638,3 +638,48 @@ NOTICE:  DROP POLICY dropped policy
 CREATE POLICY pguc ON event_trigger_test USING (FALSE);
 SET event_triggers = 'off';
 DROP POLICY pguc ON event_trigger_test;
+-- Login event triggers
+CREATE TABLE user_logins(id serial, who text);
+GRANT SELECT ON user_logins TO public;
+CREATE FUNCTION on_login_proc() RETURNS event_trigger AS $$
+BEGIN
+  INSERT INTO user_logins (who) VALUES (SESSION_USER);
+  RAISE NOTICE 'You are welcome!';
+END;
+$$ LANGUAGE plpgsql;
+CREATE EVENT TRIGGER on_login_trigger ON login EXECUTE PROCEDURE on_login_proc();
+ALTER EVENT TRIGGER on_login_trigger ENABLE ALWAYS;
+\c
+NOTICE:  You are welcome!
+SELECT COUNT(*) FROM user_logins;
+ count 
+-------
+     1
+(1 row)
+
+\c
+NOTICE:  You are welcome!
+SELECT COUNT(*) FROM user_logins;
+ count 
+-------
+     2
+(1 row)
+
+-- Check dathasloginevt in system catalog
+SELECT dathasloginevt FROM pg_database WHERE datname= :'DBNAME';
+ dathasloginevt 
+----------------
+ t
+(1 row)
+
+-- Cleanup
+DROP TABLE user_logins;
+DROP EVENT TRIGGER on_login_trigger;
+DROP FUNCTION on_login_proc();
+\c
+SELECT dathasloginevt FROM pg_database WHERE datname= :'DBNAME';
+ dathasloginevt 
+----------------
+ f
+(1 row)
+
diff --git a/src/test/regress/sql/event_trigger.sql b/src/test/regress/sql/event_trigger.sql
index 6f0933b9e88..9c2b7903fba 100644
--- a/src/test/regress/sql/event_trigger.sql
+++ b/src/test/regress/sql/event_trigger.sql
@@ -495,3 +495,29 @@ DROP POLICY pguc ON event_trigger_test;
 CREATE POLICY pguc ON event_trigger_test USING (FALSE);
 SET event_triggers = 'off';
 DROP POLICY pguc ON event_trigger_test;
+
+-- Login event triggers
+CREATE TABLE user_logins(id serial, who text);
+GRANT SELECT ON user_logins TO public;
+CREATE FUNCTION on_login_proc() RETURNS event_trigger AS $$
+BEGIN
+  INSERT INTO user_logins (who) VALUES (SESSION_USER);
+  RAISE NOTICE 'You are welcome!';
+END;
+$$ LANGUAGE plpgsql;
+CREATE EVENT TRIGGER on_login_trigger ON login EXECUTE PROCEDURE on_login_proc();
+ALTER EVENT TRIGGER on_login_trigger ENABLE ALWAYS;
+\c
+SELECT COUNT(*) FROM user_logins;
+\c
+SELECT COUNT(*) FROM user_logins;
+
+-- Check dathasloginevt in system catalog
+SELECT dathasloginevt FROM pg_database WHERE datname= :'DBNAME';
+
+-- Cleanup
+DROP TABLE user_logins;
+DROP EVENT TRIGGER on_login_trigger;
+DROP FUNCTION on_login_proc();
+\c
+SELECT dathasloginevt FROM pg_database WHERE datname= :'DBNAME';