Allow background workers to bypass datallowconn

THis adds a "flags" field to the BackgroundWorkerInitializeConnection()
and BackgroundWorkerInitializeConnectionByOid(). For now only one flag,
BGWORKER_BYPASS_ALLOWCONN, is defined, which allows the worker to ignore
datallowconn.

contrib/pg_prewarm/autoprewarm.c

@@ -445,7 +445,7 @@ autoprewarm_database_main(Datum main_arg)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
 				 errmsg("could not map dynamic shared memory segment")));
-	BackgroundWorkerInitializeConnectionByOid(apw_state->database, InvalidOid);
+	BackgroundWorkerInitializeConnectionByOid(apw_state->database, InvalidOid, 0);
 	block_info = (BlockInfoRecord *) dsm_segment_address(seg);
 	pos = apw_state->prewarm_start_idx;
 

src/backend/access/transam/parallel.c

@@ -1324,7 +1324,8 @@ ParallelWorkerMain(Datum main_arg)
 
 	/* Restore database connection. */
 	BackgroundWorkerInitializeConnectionByOid(fps->database_id,
-											  fps->authenticated_user_id);
+											  fps->authenticated_user_id,
+											  0);
 
 	/*
 	 * Set the client encoding to the database encoding, since that is what

src/backend/bootstrap/bootstrap.c

@@ -498,7 +498,7 @@ BootstrapModeMain(void)
 	 */
 	InitProcess();
 
-	InitPostgres(NULL, InvalidOid, NULL, InvalidOid, NULL);
+	InitPostgres(NULL, InvalidOid, NULL, InvalidOid, NULL, false);
 
 	/* Initialize stuff for bootstrap-file processing */
 	for (i = 0; i < MAXATTR; i++)

src/backend/postmaster/autovacuum.c

@@ -477,7 +477,7 @@ AutoVacLauncherMain(int argc, char *argv[])
 	InitProcess();
 #endif
 
-	InitPostgres(NULL, InvalidOid, NULL, InvalidOid, NULL);
+	InitPostgres(NULL, InvalidOid, NULL, InvalidOid, NULL, false);
 
 	SetProcessingMode(NormalProcessing);
 
@@ -1693,7 +1693,7 @@ AutoVacWorkerMain(int argc, char *argv[])
 		 * Note: if we have selected a just-deleted database (due to using
 		 * stale stats info), we'll fail and exit here.
 		 */
-		InitPostgres(NULL, dbid, NULL, InvalidOid, dbname);
+		InitPostgres(NULL, dbid, NULL, InvalidOid, dbname, false);
 		SetProcessingMode(NormalProcessing);
 		set_ps_display(dbname, false);
 		ereport(DEBUG1,

src/backend/postmaster/postmaster.c

@@ -5582,7 +5582,7 @@ MaxLivePostmasterChildren(void)
  * Connect background worker to a database.
  */
 void
-BackgroundWorkerInitializeConnection(const char *dbname, const char *username)
+BackgroundWorkerInitializeConnection(const char *dbname, const char *username, uint32 flags)
 {
 	BackgroundWorker *worker = MyBgworkerEntry;
 
@@ -5592,7 +5592,7 @@ BackgroundWorkerInitializeConnection(const char *dbname, const char *username)
 				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
 				 errmsg("database connection requirement not indicated during registration")));
 
-	InitPostgres(dbname, InvalidOid, username, InvalidOid, NULL);
+	InitPostgres(dbname, InvalidOid, username, InvalidOid, NULL, (flags & BGWORKER_BYPASS_ALLOWCONN) != 0);
 
 	/* it had better not gotten out of "init" mode yet */
 	if (!IsInitProcessingMode())
@@ -5605,7 +5605,7 @@ BackgroundWorkerInitializeConnection(const char *dbname, const char *username)
  * Connect background worker to a database using OIDs.
  */
 void
-BackgroundWorkerInitializeConnectionByOid(Oid dboid, Oid useroid)
+BackgroundWorkerInitializeConnectionByOid(Oid dboid, Oid useroid, uint32 flags)
 {
 	BackgroundWorker *worker = MyBgworkerEntry;
 
@@ -5615,7 +5615,7 @@ BackgroundWorkerInitializeConnectionByOid(Oid dboid, Oid useroid)
 				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
 				 errmsg("database connection requirement not indicated during registration")));
 
-	InitPostgres(NULL, dboid, NULL, useroid, NULL);
+	InitPostgres(NULL, dboid, NULL, useroid, NULL, (flags & BGWORKER_BYPASS_ALLOWCONN) != 0);
 
 	/* it had better not gotten out of "init" mode yet */
 	if (!IsInitProcessingMode())

src/backend/replication/logical/launcher.c

@@ -901,7 +901,7 @@ ApplyLauncherMain(Datum main_arg)
 	 * Establish connection to nailed catalogs (we only ever access
 	 * pg_subscription).
 	 */
-	BackgroundWorkerInitializeConnection(NULL, NULL);
+	BackgroundWorkerInitializeConnection(NULL, NULL, 0);
 
 	/* Enter main loop */
 	for (;;)

src/backend/replication/logical/worker.c

@@ -1544,7 +1544,8 @@ ApplyWorkerMain(Datum main_arg)
 
 	/* Connect to our database. */
 	BackgroundWorkerInitializeConnectionByOid(MyLogicalRepWorker->dbid,
-											  MyLogicalRepWorker->userid);
+											  MyLogicalRepWorker->userid,
+											  0);
 
 	/* Load the subscription into persistent memory context. */
 	ApplyContext = AllocSetContextCreate(TopMemoryContext,

src/backend/tcop/postgres.c

@@ -3775,7 +3775,7 @@ PostgresMain(int argc, char *argv[],
 	 * it inside InitPostgres() instead.  In particular, anything that
 	 * involves database access should be there, not here.
 	 */
-	InitPostgres(dbname, InvalidOid, username, InvalidOid, NULL);
+	InitPostgres(dbname, InvalidOid, username, InvalidOid, NULL, false);
 
 	/*
 	 * If the PostmasterContext is still around, recycle the space; we don't

src/backend/utils/init/postinit.c

@@ -66,7 +66,7 @@
 static HeapTuple GetDatabaseTuple(const char *dbname);
 static HeapTuple GetDatabaseTupleByOid(Oid dboid);
 static void PerformAuthentication(Port *port);
-static void CheckMyDatabase(const char *name, bool am_superuser);
+static void CheckMyDatabase(const char *name, bool am_superuser, bool override_allow_connections);
 static void InitCommunication(void);
 static void ShutdownPostgres(int code, Datum arg);
 static void StatementTimeoutHandler(void);
@@ -290,7 +290,7 @@ PerformAuthentication(Port *port)
  * CheckMyDatabase -- fetch information from the pg_database entry for our DB
  */
 static void
-CheckMyDatabase(const char *name, bool am_superuser)
+CheckMyDatabase(const char *name, bool am_superuser, bool override_allow_connections)
 {
 	HeapTuple	tup;
 	Form_pg_database dbform;
@@ -326,7 +326,7 @@ CheckMyDatabase(const char *name, bool am_superuser)
 		/*
 		 * Check that the database is currently allowing connections.
 		 */
-		if (!dbform->datallowconn)
+		if (!dbform->datallowconn && !override_allow_connections)
 			ereport(FATAL,
 					(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
 					 errmsg("database \"%s\" is not currently accepting connections",
@@ -563,7 +563,7 @@ BaseInit(void)
  */
 void
 InitPostgres(const char *in_dbname, Oid dboid, const char *username,
-			 Oid useroid, char *out_dbname)
+			 Oid useroid, char *out_dbname, bool override_allow_connections)
 {
 	bool		bootstrap = IsBootstrapProcessingMode();
 	bool		am_superuser;
@@ -1006,7 +1006,7 @@ InitPostgres(const char *in_dbname, Oid dboid, const char *username,
 	 * user is a superuser, so the above stuff has to happen first.)
 	 */
 	if (!bootstrap)
-		CheckMyDatabase(dbname, am_superuser);
+		CheckMyDatabase(dbname, am_superuser, override_allow_connections);
 
 	/*
 	 * Now process any command-line switches and any additional GUC variable

src/include/miscadmin.h

@@ -421,7 +421,7 @@ extern AuxProcType MyAuxProcType;
 extern void pg_split_opts(char **argv, int *argcp, const char *optstr);
 extern void InitializeMaxBackends(void);
 extern void InitPostgres(const char *in_dbname, Oid dboid, const char *username,
-			 Oid useroid, char *out_dbname);
+			 Oid useroid, char *out_dbname, bool override_allow_connections);
 extern void BaseInit(void);
 
 /* in utils/init/miscinit.c */

src/include/postmaster/bgworker.h

@@ -140,10 +140,13 @@ extern PGDLLIMPORT BackgroundWorker *MyBgworkerEntry;
  * If dbname is NULL, connection is made to no specific database;
  * only shared catalogs can be accessed.
  */
-extern void BackgroundWorkerInitializeConnection(const char *dbname, const char *username);
+extern void BackgroundWorkerInitializeConnection(const char *dbname, const char *username, uint32 flags);
 
 /* Just like the above, but specifying database and user by OID. */
-extern void BackgroundWorkerInitializeConnectionByOid(Oid dboid, Oid useroid);
+extern void BackgroundWorkerInitializeConnectionByOid(Oid dboid, Oid useroid, uint32 flags);
+
+/* Flags to BackgroundWorkerInitializeConnection et al */
+#define BGWORKER_BYPASS_ALLOWCONN 1
 
 /* Block/unblock signals in a background worker process */
 extern void BackgroundWorkerBlockSignals(void);