From: Thomas Munro <tmunro@postgresql.org>
Date: Mon, 11 Nov 2019 03:33:04 +0000 (+1300)
Subject: Optimize TransactionIdIsCurrentTransactionId().
X-Git-Url: http://git.postgresql.org/gitweb/-?a=commitdiff_plain;h=695c5977c8bc115029a85dcc1821d7b0136b4e4c;p=users%2Frhaas%2Fpostgres.git

Optimize TransactionIdIsCurrentTransactionId().

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
index fc55fa6d53..e5e2902465 100644
--- 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