v29-0002-Add-a-new-login-event-and-login-event-trigger-su.patch

From 5e0e9817cae754bb28f786ecf2435f459a5e7e81 Mon Sep 17 00:00:00 2001
From: Daniel Gustafsson <daniel@yesql.se>
Date: Mon, 14 Mar 2022 14:27:10 +0100
Subject: [PATCH v29 2/2] Add a new "login" event and login event trigger
 support.

The login event occurs when a user logs in to the system.

Author: Konstantin Knizhnik and Greg Nancarrow
Discussion: https://postgr.es/m/0d46d29f-4558-3af9-9c85-7774e14a7709%40postgrespro.ru
---
 doc/src/sgml/bki.sgml                         |   2 +-
 doc/src/sgml/catalogs.sgml                    |  13 ++
 doc/src/sgml/ecpg.sgml                        |   2 +
 doc/src/sgml/event-trigger.sgml               |  81 ++++++++-
 doc/src/sgml/ref/create_event_trigger.sgml    |   2 +-
 src/backend/commands/dbcommands.c             |   1 +
 src/backend/commands/event_trigger.c          | 156 +++++++++++++++++-
 src/backend/tcop/postgres.c                   |   4 +
 src/backend/utils/cache/evtcache.c            |   2 +
 src/backend/utils/misc/guc.c                  |   1 +
 src/backend/utils/misc/postgresql.conf.sample |   1 +
 src/bin/pg_dump/pg_dump.c                     |   5 +
 src/bin/psql/tab-complete.c                   |   3 +-
 src/include/catalog/pg_database.dat           |   2 +-
 src/include/catalog/pg_database.h             |   3 +
 src/include/commands/event_trigger.h          |   4 +-
 src/include/tcop/cmdtaglist.h                 |   1 +
 src/include/utils/evtcache.h                  |   3 +-
 src/test/recovery/t/001_stream_rep.pl         |  23 +++
 src/test/regress/expected/event_trigger.out   |  38 +++++
 src/test/regress/sql/event_trigger.sql        |  24 +++
 21 files changed, 359 insertions(+), 12 deletions(-)

diff --git a/doc/src/sgml/bki.sgml b/doc/src/sgml/bki.sgml
index 33955494c6..caef1df200 100644
--- a/doc/src/sgml/bki.sgml
+++ b/doc/src/sgml/bki.sgml
@@ -183,7 +183,7 @@
 { oid => '1', oid_symbol => 'TemplateDbOid',
   descr => 'database\'s default template',
   datname => 'template1', encoding => 'ENCODING', 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', datacl => '_null_' },
 
diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index 2a8cd02664..4dd9039b8a 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -2982,6 +2982,19 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</replaceable>:<replaceable>&l
       </para></entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>dathasloginevt</structfield> <type>bool</type>
+      </para>
+      <para>
+        Indicates that there are login event triggers defined for this database.
+        This flag is used to avoid extra lookups on the
+        <structname>pg_event_trigger</structname> table during each backend
+        startup.  This flag is used internally by <productname>PostgreSQL</productname>
+        and should not be manually altered or read for monitoring purposes.
+      </para></entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>datconnlimit</structfield> <type>int4</type>
diff --git a/doc/src/sgml/ecpg.sgml b/doc/src/sgml/ecpg.sgml
index cdc4761c60..197b476205 100644
--- a/doc/src/sgml/ecpg.sgml
+++ b/doc/src/sgml/ecpg.sgml
@@ -4731,6 +4731,7 @@ datdba = 10 (type: 1)
 encoding = 0 (type: 5)
 datistemplate = t (type: 1)
 datallowconn = t (type: 1)
+dathasloginevt = f (type: 1)
 datconnlimit = -1 (type: 5)
 datfrozenxid = 379 (type: 1)
 dattablespace = 1663 (type: 1)
@@ -4755,6 +4756,7 @@ datdba = 10 (type: 1)
 encoding = 0 (type: 5)
 datistemplate = f (type: 1)
 datallowconn = t (type: 1)
+dathasloginevt = f (type: 1)
 datconnlimit = -1 (type: 5)
 datfrozenxid = 379 (type: 1)
 dattablespace = 1663 (type: 1)
diff --git a/doc/src/sgml/event-trigger.sgml b/doc/src/sgml/event-trigger.sgml
index 9c66f97b0f..b568f3b2aa 100644
--- a/doc/src/sgml/event-trigger.sgml
+++ b/doc/src/sgml/event-trigger.sgml
@@ -28,6 +28,7 @@
      An event trigger fires whenever the event with which it is associated
      occurs in the database in which it is defined. Currently, the only
      supported events are
+     <literal>login</literal>,
      <literal>ddl_command_start</literal>,
      <literal>ddl_command_end</literal>,
      <literal>table_rewrite</literal>
@@ -35,6 +36,18 @@
      Support for additional events may be added in future releases.
    </para>
 
+   <para>
+     The <literal>login</literal> event occurs when a user logs in to the
+     system.
+     Any bugs in a trigger procedure for this event may prevent successful
+     login to the system. Such bugs may be fixed after first reconnecting to
+     the system with event triggers disabled (see <xref linkend="guc-ignore-event-trigger"/>)
+     or using restarting the system in single-user mode (as event triggers are
+     disabled in this mode).
+     See the <xref linkend="app-postgres"/> reference page for details about
+     using single-user mode.
+   </para>
+
    <para>
      The <literal>ddl_command_start</literal> event occurs just before the
      execution of a <literal>CREATE</literal>, <literal>ALTER</literal>, <literal>DROP</literal>,
@@ -1156,7 +1169,7 @@ typedef struct EventTriggerData
   </sect1>
 
   <sect1 id="event-trigger-example">
-   <title>A Complete Event Trigger Example</title>
+   <title>A C language Event Trigger Example</title>
 
    <para>
     Here is a very simple example of an event trigger function written in C.
@@ -1296,6 +1309,72 @@ $$;
 CREATE EVENT TRIGGER no_rewrite_allowed
                   ON table_rewrite
    EXECUTE FUNCTION no_rewrite();
+</programlisting>
+   </para>
+ </sect1>
+
+  <sect1 id="event-trigger-database-login-example">
+   <title>A Database Login Event Trigger Example</title>
+
+   <para>
+    The event trigger on the <literal>login</literal> event can be
+    useful for logging user logins, for verifying the connection and
+    assigning roles according to current circumstances, or for some session
+    data initialization. It is vital that any event trigger using the
+    <literal>login</literal> event checks whether or not the database is in
+    recovery.
+   </para>
+
+   <para>
+    The following example demonstrates these options.
+<programlisting>
+-- create test tables and roles
+CREATE TABLE user_login_log (
+  "user" text,
+  "session_start" timestamp with time zone
+);
+CREATE ROLE day_worker;
+CREATE ROLE night_worker;
+
+-- the example trigger function
+CREATE OR REPLACE FUNCTION init_session()
+  RETURNS event_trigger SECURITY DEFINER
+  LANGUAGE plpgsql AS
+$$
+DECLARE
+  hour integer = EXTRACT('hour' FROM current_time);
+  rec boolean;
+BEGIN
+-- Ensure the database is not in recovery
+SELECT pg_is_in_recovery() INTO rec;
+IF rec THEN
+  RETURN;
+END IF
+
+-- 1) Assign some roles
+IF hour BETWEEN 8 AND 20 THEN         -- at daytime grant the day_worker role
+  EXECUTE 'REVOKE night_worker FROM ' || quote_ident(session_user);
+  EXECUTE 'GRANT    day_worker TO '   || quote_ident(session_user);
+ELSIF hour BETWEEN 2 AND 4 THEN
+  RAISE EXCEPTION 'Login forbidden';  -- do not allow to login these hours
+ELSE                                  -- at other time grant the night_worker role
+  EXECUTE 'REVOKE day_worker FROM ' || quote_ident(session_user);
+  EXECUTE 'GRANT  night_worker TO ' || quote_ident(session_user);
+END IF;
+
+-- 2) Initialize some user session data
+CREATE TEMP TABLE session_storage (x float, y integer);
+
+-- 3) Log the connection time
+INSERT INTO user_login_log VALUES (session_user, current_timestamp);
+
+END;
+$$;
+
+-- trigger definition
+CREATE EVENT TRIGGER init_session
+  ON login
+  EXECUTE FUNCTION init_session();
 </programlisting>
    </para>
  </sect1>
diff --git a/doc/src/sgml/ref/create_event_trigger.sgml b/doc/src/sgml/ref/create_event_trigger.sgml
index 1a78555c64..92c376b8e7 100644
--- a/doc/src/sgml/ref/create_event_trigger.sgml
+++ b/doc/src/sgml/ref/create_event_trigger.sgml
@@ -125,7 +125,7 @@ CREATE EVENT TRIGGER <replaceable class="parameter">name</replaceable>
    database so much that you can't even drop the trigger, restart in
    single-user mode and you'll be able to do that. Even triggers can also be
    temporarily disabled for such troubleshooting, see
-   <xref linkend="gux-ignore-event-trigger"/>.
+   <xref linkend="guc-ignore-event-trigger"/>.
   </para>
  </refsect1>
 
diff --git a/src/backend/commands/dbcommands.c b/src/backend/commands/dbcommands.c
index 623e5ec778..08871ec5e0 100644
--- a/src/backend/commands/dbcommands.c
+++ b/src/backend/commands/dbcommands.c
@@ -712,6 +712,7 @@ 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(false);
 	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);
diff --git a/src/backend/commands/event_trigger.c b/src/backend/commands/event_trigger.c
index 70995cfc49..4e2e6629bd 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
@@ -134,6 +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),
@@ -297,6 +302,30 @@ 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 allow
+	 * faster lookups in hot codepaths. Set the flag unless already True.
+	 */
+	if (strcmp(eventname, "login") == 0)
+	{
+		Form_pg_database db;
+		Relation	pg_db = table_open(DatabaseRelationId, RowExclusiveLock);
+
+		/* Set dathasloginevt flag in pg_database */
+		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);
+	}
+
 	/* Depend on owner. */
 	recordDependencyOnOwner(EventTriggerRelationId, trigoid, evtOwner);
 
@@ -584,10 +613,15 @@ EventTriggerCommonSetup(Node *parsetree,
 	{
 		CommandTag	dbgtag;
 
-		dbgtag = CreateCommandTag(parsetree);
+		if (event == EVT_Login)
+			dbgtag = CMDTAG_LOGIN;
+		else
+			dbgtag = CreateCommandTag(parsetree);
+
 		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));
@@ -606,7 +640,10 @@ EventTriggerCommonSetup(Node *parsetree,
 		return NIL;
 
 	/* Get the command tag. */
-	tag = CreateCommandTag(parsetree);
+	if (event == EVT_Login)
+		tag = CMDTAG_LOGIN;
+	else
+		tag = CreateCommandTag(parsetree);
 
 	/*
 	 * Filter list of event triggers by command tag, and copy them into our
@@ -807,6 +844,112 @@ EventTriggerSQLDrop(Node *parsetree)
 	list_free(runlist);
 }
 
+/*
+ * Return true if this database has login event triggers, false otherwise.
+ */
+static bool
+DatabaseHasLoginEventTriggers(void)
+{
+	bool		has_login_event_triggers;
+	HeapTuple	tuple = SearchSysCache1(DATABASEOID, ObjectIdGetDatum(MyDatabaseId));
+
+	if (!HeapTupleIsValid(tuple))
+		elog(ERROR, "cache lookup failed for database %u", MyDatabaseId);
+
+	has_login_event_triggers = ((Form_pg_database) GETSTRUCT(tuple))->dathasloginevt;
+	ReleaseSysCache(tuple);
+	return has_login_event_triggers;
+}
+
+/*
+ * 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.
+	 */
+	if (!IsUnderPostmaster || !OidIsValid(MyDatabaseId)
+		|| ignore_event_trigger_check(EVT_Login))
+		return;
+
+	StartTransactionCommand();
+
+	if (DatabaseHasLoginEventTriggers())
+	{
+		runlist = EventTriggerCommonSetup(NULL,
+										  EVT_Login, "login",
+										  &trigdata);
+
+		if (runlist != NIL)
+		{
+			/*
+			 * Event trigger execution may require an active snapshot.
+			 */
+			PushActiveSnapshot(GetTransactionSnapshot());
+
+			/* Run the triggers. */
+			EventTriggerInvoke(runlist, &trigdata);
+
+			/* Cleanup. */
+			list_free(runlist);
+
+			PopActiveSnapshot();
+		}
+		else
+		{
+			/*
+			 * Runlist is empty: clear dathasloginevt flag
+			 */
+			Relation	pg_db = table_open(DatabaseRelationId, RowExclusiveLock);
+			HeapTuple	tuple;
+			Form_pg_database db;
+
+			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)
+			{
+				/*
+				 * There can be a race condition: a login event trigger may
+				 * have been added after the pg_event_trigger table was
+				 * scanned, and we don't want to erroneously clear the
+				 * dathasloginevt flag in this case. To be sure that this
+				 * hasn't happened, repeat the scan under the pg_database
+				 * table lock.
+				 */
+				runlist = EventTriggerCommonSetup(NULL,
+												  EVT_Login, "login",
+												  &trigdata);
+				if (runlist == NIL)	/* list is still empty, so clear the
+										 * flag */
+				{
+					db->dathasloginevt = false;
+					CatalogTupleUpdate(pg_db, &tuple->t_self, tuple);
+				}
+				else
+					list_free(runlist);
+			}
+			table_close(pg_db, RowExclusiveLock);
+			heap_freetuple(tuple);
+		}
+	}
+	CommitTransactionCommand();
+}
+
 
 /*
  * Fire table_rewrite triggers.
@@ -2186,8 +2329,7 @@ stringify_adefprivs_objtype(ObjectType objtype)
 
 /*
  * Checks whether the specified event is ignored by the ignore_event_trigger
- * GUC or not. Currently, the GUC only supports ignoreing all or nothing but
- * that will most likely change so the function takes an event to aid that.
+ * GUC or not.
  */
 static bool
 ignore_event_trigger_check(EventTriggerEvent event)
@@ -2197,6 +2339,10 @@ ignore_event_trigger_check(EventTriggerEvent event)
 	if (ignore_event_trigger == IGNORE_EVENT_TRIGGER_ALL)
 		return true;
 
+	if (ignore_event_trigger == IGNORE_EVENT_TRIGGER_LOGIN
+		&& event == EVT_Login)
+		return true;
+
 	/* IGNORE_EVENT_TRIGGER_NONE */
 	return false;
 
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index ba2fcfeb4a..5638cd95b2 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -41,6 +41,7 @@
 #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"
@@ -4202,6 +4203,9 @@ 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 3a9c9f0c50..43a38ae6c7 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/misc/guc.c b/src/backend/utils/misc/guc.c
index 088c4690d9..c5d53386e7 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -569,6 +569,7 @@ static const struct config_enum_entry wal_compression_options[] = {
 static const struct config_enum_entry ignore_event_trigger_options[] = {
 	{"none", IGNORE_EVENT_TRIGGER_NONE, false},
 	{"all", IGNORE_EVENT_TRIGGER_ALL, false},
+	{"login", IGNORE_EVENT_TRIGGER_LOGIN, false},
 	{NULL, 0, false}
 };
 
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 4cf5b26a36..0d7623fc7a 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -674,6 +674,7 @@
 					#   error
 #search_path = '"$user", public'	# schema names
 #row_security = on
+#ignore_event_trigger = 'none'
 #default_table_access_method = 'heap'
 #default_tablespace = ''		# a tablespace name, '' uses the default
 #default_toast_compression = 'pglz'	# 'pglz' or 'lz4'
diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index e5816c4cce..dd756ae4db 100644
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -3052,6 +3052,11 @@ 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 5c064595a9..8850324a3b 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -3395,7 +3395,8 @@ 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");
+		COMPLETE_WITH("ddl_command_start", "ddl_command_end",
+					  "login", "sql_drop");
 
 	/*
 	 * Complete CREATE EVENT TRIGGER <name> ON <event_type>.  EXECUTE FUNCTION
diff --git a/src/include/catalog/pg_database.dat b/src/include/catalog/pg_database.dat
index 5feedff7bf..78402d48bc 100644
--- a/src/include/catalog/pg_database.dat
+++ b/src/include/catalog/pg_database.dat
@@ -15,7 +15,7 @@
 { oid => '1', oid_symbol => 'TemplateDbOid',
   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', datacl => '_null_' },
 
diff --git a/src/include/catalog/pg_database.h b/src/include/catalog/pg_database.h
index a9f4a8071f..55d7ae7988 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 (-1=no limit) */
 	int32		datconnlimit;
 
diff --git a/src/include/commands/event_trigger.h b/src/include/commands/event_trigger.h
index 9e7671e63f..2400cc7d7a 100644
--- a/src/include/commands/event_trigger.h
+++ b/src/include/commands/event_trigger.h
@@ -32,7 +32,8 @@ typedef struct EventTriggerData
 typedef enum ignore_event_trigger_events
 {
 	IGNORE_EVENT_TRIGGER_NONE,
-	IGNORE_EVENT_TRIGGER_ALL
+	IGNORE_EVENT_TRIGGER_ALL,
+	IGNORE_EVENT_TRIGGER_LOGIN
 } IgnoreEventTriggersEvents;
 
 extern int ignore_event_trigger;
@@ -62,6 +63,7 @@ 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/tcop/cmdtaglist.h b/src/include/tcop/cmdtaglist.h
index 4bc7ddf410..d6e408e1ed 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_MOVE, "MOVE", false, false, true)
 PG_CMDTAG(CMDTAG_NOTIFY, "NOTIFY", false, false, false)
 PG_CMDTAG(CMDTAG_PREPARE, "PREPARE", false, false, false)
diff --git a/src/include/utils/evtcache.h b/src/include/utils/evtcache.h
index ddb67a68fa..a66344aacb 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/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl
index 583ee87da8..c3dbd75af3 100644
--- a/src/test/recovery/t/001_stream_rep.pl
+++ b/src/test/recovery/t/001_stream_rep.pl
@@ -46,6 +46,24 @@ $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
 my $primary_lsn = $node_primary->lsn('write');
 $node_primary->wait_for_catchup($node_standby_1, 'replay', $primary_lsn);
@@ -387,6 +405,11 @@ 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 44d545de25..fb2c799ebb 100644
--- a/src/test/regress/expected/event_trigger.out
+++ b/src/test/regress/expected/event_trigger.out
@@ -604,3 +604,41 @@ SELECT
 DROP EVENT TRIGGER start_rls_command;
 DROP EVENT TRIGGER end_rls_command;
 DROP EVENT TRIGGER sql_drop_command;
+-- 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();
diff --git a/src/test/regress/sql/event_trigger.sql b/src/test/regress/sql/event_trigger.sql
index 1446cf8cc8..3123cbb23d 100644
--- a/src/test/regress/sql/event_trigger.sql
+++ b/src/test/regress/sql/event_trigger.sql
@@ -462,3 +462,27 @@ SELECT
 DROP EVENT TRIGGER start_rls_command;
 DROP EVENT TRIGGER end_rls_command;
 DROP EVENT TRIGGER sql_drop_command;
+
+-- 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();
-- 
2.24.3 (Apple Git-128)