Always SnapshotResetXmin() during ClearTransaction()

Avoid corner cases during 2PC with 6bad580

Author: simonat2ndQuadrant

src/backend/access/transam/xact.c

@@ -2640,7 +2640,7 @@ CleanupTransaction(void)
 	 * do abort cleanup processing
 	 */
 	AtCleanup_Portals();		/* now safe to release portal memory */
-	AtEOXact_Snapshot(false, false); /* and release the transaction's snapshots */
+	AtEOXact_Snapshot(false, true); /* and release the transaction's snapshots */
 
 	CurrentResourceOwner = NULL;	/* and resource owner */
 	if (TopTransactionResourceOwner)

src/backend/utils/time/snapmgr.c

@@ -1051,7 +1051,7 @@ AtSubAbort_Snapshot(int level)
  *		Snapshot manager's cleanup function for end of transaction
  */
 void
-AtEOXact_Snapshot(bool isCommit, bool isPrepare)
+AtEOXact_Snapshot(bool isCommit, bool resetXmin)
 {
 	/*
 	 * In transaction-snapshot mode we must release our privately-managed
@@ -1137,16 +1137,15 @@ AtEOXact_Snapshot(bool isCommit, bool isPrepare)
 	FirstSnapshotSet = false;
 
 	/*
-	 * During normal commit and abort processing, we call
-	 * ProcArrayEndTransaction() or ProcArrayClearTransaction() to
-	 * reset the PgXact->xmin. That call happens prior to the call to
-	 * AtEOXact_Snapshot(), so we need not touch xmin here at all,
-	 * accept when we are preparing a transaction.
+	 * During normal commit processing, we call
+	 * ProcArrayEndTransaction() to reset the PgXact->xmin. That call
+	 * happens prior to the call to AtEOXact_Snapshot(), so we need
+	 * not touch xmin here at all.
 	 */
-	if (isPrepare)
+	if (resetXmin)
 		SnapshotResetXmin();
 
-	Assert(isPrepare || MyPgXact->xmin == 0);
+	Assert(resetXmin || MyPgXact->xmin == 0);
 }
 
 

src/include/utils/snapmgr.h

@@ -85,7 +85,7 @@ extern void UnregisterSnapshotFromOwner(Snapshot snapshot, ResourceOwner owner);
 
 extern void AtSubCommit_Snapshot(int level);
 extern void AtSubAbort_Snapshot(int level);
-extern void AtEOXact_Snapshot(bool isCommit, bool isPrepare);
+extern void AtEOXact_Snapshot(bool isCommit, bool resetXmin);
 
 extern void ImportSnapshot(const char *idstr);
 extern bool XactHasExportedSnapshots(void);