Adjust assertion in GetCurrentCommandId.

robertmhaas · robertmhaas · commit cce1ecfc7738 · 2017-12-21T13:19:59.000-05:00
currentCommandIdUsed is only used to skip redundant increments of the command counter, and CommandCounterIncrement() is categorically denied under parallelism anyway. Therefore, it's OK for GetCurrentCommandId() to mark the counter value used, as long as it happens in the leader, not a worker. Prior to commit e9baa5e, the slightly incorrect check didn't matter, but now it does. A test case added by commit 1804284 uncovered the problem by accident; it caused failures with force_parallel_mode=on/regress. Report and review by Andres Freund. Patch by me. Discussion: http://postgr.es/m/20171221143106.5lhtygohvmazli3x@alap3.anarazel.de
diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
@@ -683,12 +683,12 @@ GetCurrentCommandId(bool used)
 	if (used)
 	{
 		/*
-		 * Forbid setting currentCommandIdUsed in parallel mode, because we
-		 * have no provision for communicating this back to the master.  We
+		 * Forbid setting currentCommandIdUsed in a parallel worker, because
+		 * we have no provision for communicating this back to the master.  We
 		 * could relax this restriction when currentCommandIdUsed was already
 		 * true at the start of the parallel operation.
 		 */
-		Assert(CurrentTransactionState->parallelModeLevel == 0);
+		Assert(!IsParallelWorker());
 		currentCommandIdUsed = true;
 	}
 	return currentCommandId;
