Change overly strict Assert in TransactionGroupUpdateXidStatus.

Amit Kapila · Amit Kapila · commit af3290f5e790 · 2019-12-17T09:29:22.000+05:30
This Assert thought that an overflowed transaction can never get registered for the group update. But that is not true, because even when the number of children for a transaction got reduced, the overflow flag is not changed. And, for group update, we only care about the current number of children for a transaction that is being committed. Based on comments by Andres Freund, remove a redundant Assert in TransactionIdSetPageStatus as we already had a static Assert for the same condition a few lines earlier. Reported-by: Vignesh C Author: Dilip Kumar Reviewed-by: Amit Kapila Backpatch-through: 11 Discussion: https://postgr.es/m/CAFiTN-s5=uJw-Z6JC9gcqtBSjXsrHnU63PXBrA=pnBjqnkm5UA@mail.gmail.com
diff --git a/src/backend/access/transam/clog.c b/src/backend/access/transam/clog.c
@@ -299,13 +299,6 @@ TransactionIdSetPageStatus(TransactionId xid, int nsubxids,
 		memcmp(subxids, MyProc->subxids.xids,
 			   nsubxids * sizeof(TransactionId)) == 0)
 	{
-		/*
-		 * We don't try to do group update optimization if a process has
-		 * overflowed the subxids array in its PGPROC, since in that case we
-		 * don't have a complete list of XIDs for it.
-		 */
-		Assert(THRESHOLD_SUBTRANS_CLOG_OPT <= PGPROC_MAX_CACHED_SUBXIDS);
-
 		/*
 		 * If we can immediately acquire CLogControlLock, we update the status
 		 * of our own XID and release the lock.  If not, try use group XID
@@ -520,10 +513,10 @@ TransactionGroupUpdateXidStatus(TransactionId xid, XidStatus status,
 		PGXACT	   *pgxact = &ProcGlobal->allPgXact[nextidx];
 
 		/*
-		 * Overflowed transactions should not use group XID status update
-		 * mechanism.
+		 * Transactions with more than THRESHOLD_SUBTRANS_CLOG_OPT sub-XIDs
+		 * should not use group XID status update mechanism.
 		 */
-		Assert(!pgxact->overflowed);
+		Assert(pgxact->nxids <= THRESHOLD_SUBTRANS_CLOG_OPT);
 
 		TransactionIdSetPageStatusInternal(proc->clogGroupMemberXid,
 										   pgxact->nxids,
