Optimize TransactionIdIsCurrentTransactionId().

macdice · macdice · commit 695c5977c8bc · 2019-11-11T16:33:04.000+13:00
If the passed in xid is the current top transaction, we can do a fast check and exit early. This should work well for the current heap but also works very well for proposed AMs that don't use a separate xid for subtransactions. Author: Ashwin Agrawal, based on a suggestion from Andres Freund Reviewed-by: Thomas Munro Discussion: https://postgr.es/m/CALfoeiv0k3hkEb3Oqk%3DziWqtyk2Jys1UOK5hwRBNeANT_yX%2Bng%40mail.gmail.com
diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
@@ -871,6 +871,9 @@ TransactionIdIsCurrentTransactionId(TransactionId xid)
 	if (!TransactionIdIsNormal(xid))
 		return false;
 
+	if (TransactionIdEquals(xid, GetTopTransactionIdIfAny()))
+		return true;
+
 	/*
 	 * In parallel workers, the XIDs we must consider as current are stored in
 	 * ParallelCurrentXids rather than the transaction-state stack.  Note that
