allow replication session to be set in several backends

Author: kelvich

contrib/mmts/multimaster.c

@@ -3817,7 +3817,7 @@ void MtmSetupReplicationHooks(struct PGLogicalHooks* hooks)
  */
 void MtmBeginSession(int nodeId)
 {
-	MtmLockNode(nodeId, LW_EXCLUSIVE);
+	// MtmLockNode(nodeId, LW_EXCLUSIVE);
 	Assert(replorigin_session_origin == InvalidRepOriginId);
 	replorigin_session_origin = Mtm->nodes[nodeId-1].originId;
 	Assert(replorigin_session_origin != InvalidRepOriginId);
@@ -3837,9 +3837,9 @@ void MtmEndSession(int nodeId, bool unlock)
 		replorigin_session_origin_lsn = INVALID_LSN;
 		replorigin_session_origin_timestamp = 0;
 		replorigin_session_reset();
-		if (unlock) {
-			MtmUnlockNode(nodeId);
-		}
+		// if (unlock) {
+		// 	MtmUnlockNode(nodeId);
+		// }
 		MTM_LOG3("%d: End reset replorigin session: %d", MyProcPid, replorigin_session_origin);
 	}
 }

src/backend/replication/logical/origin.c

@@ -1029,13 +1029,20 @@ replorigin_session_setup(RepOriginId node)
 		if (curstate->roident != node)
 			continue;
 
-		else if (curstate->acquired_by != 0)
-		{
-			ereport(ERROR,
-					(errcode(ERRCODE_OBJECT_IN_USE),
-			 errmsg("replication identifier %d is already active for PID %d",
-					curstate->roident, curstate->acquired_by)));
-		}
+		/*
+		 * MTM-CRUTCH.
+		 *
+		 * Allow multiple backends to setup same replication session.
+		 *
+		 * else if (curstate->acquired_by != 0)
+		 * {
+		 * 	ereport(ERROR,
+		 * 			(errcode(ERRCODE_OBJECT_IN_USE),
+		 * 	 errmsg("replication identifier %d is already active for PID %d",
+		 * 			curstate->roident, curstate->acquired_by)));
+		 * }
+		 *
+		 */
 
 		/* ok, found slot */
 		session_replication_state = curstate;