From 090e8a984cf1a8a3ef7f6db6dc919f843902d80c Mon Sep 17 00:00:00 2001
From: Simon Riggs <simon@2ndQuadrant.com>
Date: Thu, 7 Jun 2012 19:26:03 +0100
Subject: [PATCH] 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, allowing
significantly reduced data loss at failover.
Andres Freund and Simon Riggs
---
src/backend/access/transam/xlog.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 3902c58313..64d7660b38 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -2115,6 +2115,7 @@ XLogBackgroundFlush(void)
{
XLogRecPtr WriteRqstPtr;
bool flexible = true;
+ bool wrote_something = false;
/* XLOG doesn't need flushing during recovery */
if (RecoveryInProgress())
@@ -2183,10 +2184,18 @@ XLogBackgroundFlush(void)
WriteRqst.Write = WriteRqstPtr;
WriteRqst.Flush = WriteRqstPtr;
XLogWrite(WriteRqst, flexible, false);
+ wrote_something = true;
}
LWLockRelease(WALWriteLock);
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();
}
/*
--
2.49.0