Backend support for streaming base backups

Add BASE_BACKUP command to walsender, allowing it to stream a
base backup to the client (in tar format). The syntax is still
far from ideal, that will be fixed in the switch to use a proper
grammar for walsender.

No client included yet, will come as a separate commit.

Magnus Hagander and Heikki Linnakangas

src/backend/replication/walsender.c

@@ -44,6 +44,7 @@
 #include "libpq/pqformat.h"
 #include "libpq/pqsignal.h"
 #include "miscadmin.h"
+#include "replication/basebackup.h"
 #include "replication/walprotocol.h"
 #include "replication/walsender.h"
 #include "storage/fd.h"
@@ -54,6 +55,7 @@
 #include "utils/guc.h"
 #include "utils/memutils.h"
 #include "utils/ps_status.h"
+#include "utils/resowner.h"
 
 
 /* Array of WalSnds in shared memory */
@@ -136,6 +138,9 @@ WalSenderMain(void)
 										   ALLOCSET_DEFAULT_MAXSIZE);
 	MemoryContextSwitchTo(walsnd_context);
 
+	/* Set up resource owner */
+	CurrentResourceOwner = ResourceOwnerCreate(NULL, "walsender top-level resource owner");
+
 	/* Unblock signals (they were blocked when the postmaster forked us) */
 	PG_SETMASK(&UnBlockSig);
 
@@ -305,6 +310,15 @@ WalSndHandshake(void)
 						/* break out of the loop */
 						replication_started = true;
 					}
+					else if (strncmp(query_string, "BASE_BACKUP ", 12) == 0)
+					{
+						/* Command is BASE_BACKUP <options>;<label> */
+						SendBaseBackup(query_string + strlen("BASE_BACKUP "));
+						/* Send CommandComplete and ReadyForQuery messages */
+						EndCommand("SELECT", DestRemote);
+						ReadyForQuery(DestRemote);
+						/* ReadyForQuery did pq_flush for us */
+					}
 					else
 					{
 						ereport(FATAL,