From: Simon Riggs <simon@2ndQuadrant.com>
Date: Thu, 7 Jun 2012 18:22:47 +0000 (+0100)
Subject: Wake WALSender to reduce data loss at failover for async commit.
X-Git-Tag: REL9_2_BETA3~129
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=2c8a4e9be2730342cbca85150a2a9d876aa77ff6;p=postgresql

Wake WALSender to reduce data loss at failover for async commit.
WALSender now woken up after each background flush by WALwriter, avoiding
multi-second replication delay for an all-async commit workload.
Replication delay reduced from 7s with default settings to 200ms and often
much less, allowing significantly reduced data loss at failover.

Andres Freund and Simon Riggs
---

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index d3650bdf05..0f2678cfda 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -2271,6 +2271,13 @@ XLogBackgroundFlush(void)
 
 	END_CRIT_SECTION();
 
+	/*
+	 * If we wrote something then we have something to send to standbys also,
+	 * otherwise the replication delay become around 7s with just async commit.
+	 */
+	if (wrote_something)
+		WalSndWakeup();
+
 	return wrote_something;
 }