Fix cursor snapshot dump xid issue

For cursor snapshot dump, we need to record both distributed and local
xid. So far, we only record distributed xid in the dump, as well as,
incorrectly assign distributed xid to local xid by dump read function.

Fix it.

src/backend/access/transam/xact.c

@@ -2435,7 +2435,7 @@ StartTransaction(void)
 				SharedLocalSnapshotSlot->ready = false;
 				SharedLocalSnapshotSlot->xid = s->transactionId;
 				SharedLocalSnapshotSlot->startTimestamp = stmtStartTimestamp;
-				SharedLocalSnapshotSlot->QDxid = QEDtxContextInfo.distributedXid;
+				SharedLocalSnapshotSlot->distributedXid = QEDtxContextInfo.distributedXid;
 				SharedLocalSnapshotSlot->writer_proc = MyProc;
 				SharedLocalSnapshotSlot->writer_xact = MyPgXact;
 
@@ -2446,7 +2446,7 @@ StartTransaction(void)
 							  " (shared timeStamp = " INT64_FORMAT " -> "
 							  INT64_FORMAT ")",
 							  QEDtxContextInfo.distributedXid,
-							  SharedLocalSnapshotSlot->QDxid,
+							  SharedLocalSnapshotSlot->distributedXid,
 							  SharedLocalSnapshotSlot->xid,
 							  s->transactionId,
 							  SharedLocalSnapshotSlot->ready ? "true" : "false",
@@ -3620,7 +3620,7 @@ StartTransactionCommand(void)
 				}
 
 				SharedLocalSnapshotSlot->startTimestamp = xactStartTimestamp;
-				SharedLocalSnapshotSlot->QDxid = QEDtxContextInfo.distributedXid;
+				SharedLocalSnapshotSlot->distributedXid = QEDtxContextInfo.distributedXid;
 
 				LWLockRelease(SharedLocalSnapshotSlot->slotLock);
 

src/backend/cdb/cdbtm.c

@@ -1671,7 +1671,7 @@ setupQEDtxContext(DtxContextInfo *dtxContextInfo)
 					 SharedLocalSnapshotSlot->snapshot.xmax,
 					 SharedLocalSnapshotSlot->snapshot.xcnt,
 					 SharedLocalSnapshotSlot->snapshot.curcid,
-					 SharedLocalSnapshotSlot->QDxid,
+					 SharedLocalSnapshotSlot->distributedXid,
 					 SharedLocalSnapshotSlot->segmateSync);
 				LWLockRelease(SharedLocalSnapshotSlot->slotLock);
 			}

src/backend/storage/ipc/procarray.c

@@ -1625,7 +1625,7 @@ updateSharedLocalSnapshot(DtxContextInfo *dtxContextInfo,
 
 	SetSharedTransactionId_writer(distributedTransactionContext);
 	
-	SharedLocalSnapshotSlot->QDxid = dtxContextInfo->distributedXid;
+	SharedLocalSnapshotSlot->distributedXid = dtxContextInfo->distributedXid;
 	SharedLocalSnapshotSlot->segmateSync = dtxContextInfo->segmateSync;
 	SharedLocalSnapshotSlot->ready = true;
 
@@ -1637,12 +1637,12 @@ updateSharedLocalSnapshot(DtxContextInfo *dtxContextInfo,
 					SharedLocalSnapshotSlot->snapshot.xmax,
 					SharedLocalSnapshotSlot->snapshot.xcnt,
 					SharedLocalSnapshotSlot->snapshot.curcid,
-					SharedLocalSnapshotSlot->QDxid)));
+					SharedLocalSnapshotSlot->distributedXid)));
 
 	ereport((Debug_print_snapshot_dtm ? LOG : DEBUG5),
 			(errmsg("[Distributed Snapshot #%u] *Writer Set Shared* gxid %u, (gxid = %u, slot #%d, '%s', '%s')",
 					QEDtxContextInfo.distributedSnapshot.distribSnapshotId,
-					SharedLocalSnapshotSlot->QDxid,
+					SharedLocalSnapshotSlot->distributedXid,
 					getDistributedTransactionId(),
 					SharedLocalSnapshotSlot->slotid,
 					debugCaller,
@@ -1758,10 +1758,10 @@ readerFillLocalSnapshot(Snapshot snapshot, DtxContext distributedTransactionCont
 		if (QEDtxContextInfo.segmateSync == SharedLocalSnapshotSlot->segmateSync &&
 			SharedLocalSnapshotSlot->ready)
 		{
-			if (QEDtxContextInfo.distributedXid != SharedLocalSnapshotSlot->QDxid)
+			if (QEDtxContextInfo.distributedXid != SharedLocalSnapshotSlot->distributedXid)
 				elog(ERROR, "transaction ID doesn't match between the reader gang "
 							"and the writer gang, expect %d but having %d",
-							QEDtxContextInfo.distributedXid, SharedLocalSnapshotSlot->QDxid);
+							QEDtxContextInfo.distributedXid, SharedLocalSnapshotSlot->distributedXid);
 			copyLocalSnapshot(snapshot);
 			SetSharedTransactionId_reader(SharedLocalSnapshotSlot->xid, snapshot->curcid, distributedTransactionContext);
 			LWLockRelease(SharedLocalSnapshotSlot->slotLock);
@@ -1780,7 +1780,7 @@ readerFillLocalSnapshot(Snapshot snapshot, DtxContext distributedTransactionCont
 							   "DistributedTransactionContext = %s. "
 							   " Our slotindex is: %d \n"
 							   "Dump of all sharedsnapshots in shmem: %s",
-							   QEDtxContextInfo.distributedXid, SharedLocalSnapshotSlot->QDxid,
+							   QEDtxContextInfo.distributedXid, SharedLocalSnapshotSlot->distributedXid,
 							   QEDtxContextInfo.segmateSync,
 							   SharedLocalSnapshotSlot->segmateSync, SharedLocalSnapshotSlot->ready,
 							   DtxContextToString(distributedTransactionContext),
@@ -1796,7 +1796,7 @@ readerFillLocalSnapshot(Snapshot snapshot, DtxContext distributedTransactionCont
 					(errmsg("[Distributed Snapshot #%u] *No Match* gxid %u = %u and segmateSync %d = %d (%s)",
 							QEDtxContextInfo.distributedSnapshot.distribSnapshotId,
 							QEDtxContextInfo.distributedXid,
-							SharedLocalSnapshotSlot->QDxid,
+							SharedLocalSnapshotSlot->distributedXid,
 							QEDtxContextInfo.segmateSync,
 							SharedLocalSnapshotSlot->segmateSync,
 							DtxContextToString(distributedTransactionContext))));
@@ -1808,7 +1808,7 @@ readerFillLocalSnapshot(Snapshot snapshot, DtxContext distributedTransactionCont
 							" Our slotindex is: %d \n"
 							"DistributedTransactionContext = %s.",
 							QEDtxContextInfo.distributedXid, QEDtxContextInfo.segmateSync,
-							SharedLocalSnapshotSlot->QDxid, SharedLocalSnapshotSlot->segmateSync,
+							SharedLocalSnapshotSlot->distributedXid, SharedLocalSnapshotSlot->segmateSync,
 							SharedLocalSnapshotSlot->ready,
 							SharedLocalSnapshotSlot->slotindex,
 							DtxContextToString(distributedTransactionContext))));
@@ -3140,12 +3140,12 @@ UpdateSerializableCommandId(CommandId curcid)
 	{
 		LWLockAcquire(SharedLocalSnapshotSlot->slotLock, LW_EXCLUSIVE);
 
-		if (SharedLocalSnapshotSlot->QDxid != QEDtxContextInfo.distributedXid)
+		if (SharedLocalSnapshotSlot->distributedXid != QEDtxContextInfo.distributedXid)
 		{
 			ereport((Debug_print_snapshot_dtm ? LOG : DEBUG5),
 					(errmsg("[Distributed Snapshot #%u] *Can't Update Serializable Command Id* QDxid = %u (gxid = %u, '%s')",
 							QEDtxContextInfo.distributedSnapshot.distribSnapshotId,
-							SharedLocalSnapshotSlot->QDxid,
+							SharedLocalSnapshotSlot->distributedXid,
 							getDistributedTransactionId(),
 							DtxContextToString(DistributedTransactionContext))));
 			LWLockRelease(SharedLocalSnapshotSlot->slotLock);

src/backend/utils/time/sharedsnapshot.c

@@ -350,7 +350,7 @@ SharedSnapshotDump(void)
 		if (testSlot->slotid != -1)
 		{
 			appendStringInfo(&str, "(SLOT index: %d slotid: %d QDxid: %u pid: %u)",
-							 testSlot->slotindex, testSlot->slotid, testSlot->QDxid,
+							 testSlot->slotindex, testSlot->slotid, testSlot->distributedXid,
 							 testSlot->writer_proc ? testSlot->writer_proc->pid : 0);
 		}
 
@@ -462,7 +462,7 @@ retry:
 	slot->slotid = slotId;
 	slot->xid = 0;
 	slot->startTimestamp = 0;
-	slot->QDxid = 0;
+	slot->distributedXid = 0;
 	slot->segmateSync = 0;
 	/* Remember the writer proc for IsCurrentTransactionIdForReader */
 	slot->writer_proc = MyProc;
@@ -573,7 +573,7 @@ SharedSnapshotRemove(volatile SharedSnapshotSlot *slot, char *creatorDescription
 	slot->slotid = -1;
 	slot->xid = 0;
 	slot->startTimestamp = 0;
-	slot->QDxid = 0;
+	slot->distributedXid = 0;
 	slot->segmateSync = 0;
 
 	sharedSnapshotArray->numSlots -= 1;
@@ -672,7 +672,8 @@ dumpSharedLocalSnapshot_forCursor(void)
 	pDump->segment = segment;
 	pDump->handle = dsm_segment_handle(segment);
 	pDump->segmateSync = src->segmateSync;
-	pDump->xid = src->QDxid;
+	pDump->distributedXid = src->distributedXid;
+	pDump->localXid = src->xid;
 
 	elog(LOG, "Dump syncmate : %u snapshot to slot %d", src->segmateSync, id);
 
@@ -725,7 +726,7 @@ readSharedLocalSnapshot_forCursor(Snapshot snapshot, DtxContext distributedTrans
 				search_iter = SNAPSHOTDUMPARRAYSZ - 1;
 
 			if(src->dump[search_iter].segmateSync == QEDtxContextInfo.segmateSync &&
-				src->dump[search_iter].xid == QEDtxContextInfo.distributedXid)
+				src->dump[search_iter].distributedXid == QEDtxContextInfo.distributedXid)
 			{
 				pDump = &src->dump[search_iter];
 				found = true;
@@ -751,7 +752,7 @@ readSharedLocalSnapshot_forCursor(Snapshot snapshot, DtxContext distributedTrans
 		char *ptr = dsm_segment_address(segment);
 
 		entry->snapshot = RestoreSnapshot(ptr);
-		entry->localXid = pDump->xid;
+		entry->localXid = pDump->localXid;
 
 
 		dsm_detach(segment);

src/include/utils/sharedsnapshot.h

@@ -20,7 +20,8 @@
 typedef struct SnapshotDump
 {
 	uint32 segmateSync;
-	TransactionId xid;
+	DistributedTransactionId distributedXid;
+	TransactionId localXid;
 	dsm_handle  handle;
 	dsm_segment *segment;
 } SnapshotDump;
@@ -34,7 +35,10 @@ typedef struct SharedSnapshotSlot
 	int32	 		slotid;
 	PGPROC			*writer_proc;
 	PGXACT			*writer_xact;
-	volatile TransactionId   QDxid;
+
+	/* only used by cursor dump identification, dose not always set */
+	volatile DistributedTransactionId distributedXid;
+
 	volatile bool			ready;
 	volatile uint32			segmateSync;
 	SnapshotData	snapshot;