handle aborted tx state in MtmExplicitPrepare

Author: kelvich

expected/multimaster.out

@@ -349,6 +349,10 @@ commit prepared 'y';
 ERROR:  COMMIT PREPARED cannot run inside a transaction block
 rollback;
 commit prepared 'y';
+begin;
+select 1/0;
+ERROR:  division by zero
+prepare transaction 'noprep';
 table twopc_test;
  i 
 ---

sql/multimaster.sql

@@ -251,6 +251,10 @@ rollback;
 
 commit prepared 'y';
 
+begin;
+select 1/0;
+prepare transaction 'noprep';
+
 table twopc_test;
 table twopc_test2;
 

src/commit.c

@@ -483,6 +483,17 @@ MtmExplicitPrepare(char *gid)
 	int			n_messages;
 	int			i;
 
+	/*
+	 * GetTopTransactionId() will fail for aborted tx, but we still need to
+	 * finish it, so handle that manually.
+	 */
+	if (IsAbortedTransactionBlockState())
+	{
+		ret = PrepareTransactionBlock(gid);
+		Assert(!ret);
+		return false;
+	}
+
 	xid = GetTopTransactionId();
 	sprintf(stream, "xid" XID_FMT, xid);
 	dmq_stream_subscribe(stream);