PGPRO-1964: disable autovacum in snapshot

Author: knizhnik

src/backend/postmaster/autovacuum.c

@@ -1702,7 +1702,10 @@ AutoVacWorkerMain(int argc, char *argv[])
 		/* And do an appropriate amount of work */
 		recentXid = ReadNewTransactionId();
 		recentMulti = ReadNextMultiXactId();
+
+		LWLockAcquire(DoAutovacuumLock, LW_SHARED);
 		do_autovacuum();
+		LWLockRelease(DoAutovacuumLock);
 	}
 
 	/*

src/backend/storage/file/snapfs.c

@@ -167,7 +167,9 @@ sfs_switch_to_snapshot(SnapshotId snap_id)
 	if (!SFS_IN_SNAPSHOT())
 		sfs_checkpoint();
 
+	LWLockAcquire(DoAutovacuumLock, LW_EXCLUSIVE); /* prevenyt autovacuum in snapshot */
 	ControlFile->active_snapshot = snap_id;
+	LWLockRelease(DoAutovacuumLock);
 	UpdateControlFile();
 
 	DropSharedBuffers();

src/backend/storage/lmgr/lwlocknames.txt

@@ -50,3 +50,5 @@ OldSnapshotTimeMapLock				42
 BackendRandomLock					43
 LogicalRepWorkerLock				44
 CLogTruncationLock					45
+DoAutovacuumLock					46
+