From 5787c6730e7a848ef95d5c4194e27614ea8e6e41 Mon Sep 17 00:00:00 2001
From: Simon Riggs <simon@2ndQuadrant.com>
Date: Mon, 8 Apr 2013 09:11:49 +0100
Subject: [PATCH] Skip extraneous locking in XLogCheckBuffer(). Heikki reported
comment was wrong, so fixed code to match the comment: we only need to take
additional locking precautions when we have a shared lock on the buffer.
---
src/backend/access/transam/xlog.c | 27 ++++++++++++++++-----------
1 file changed, 16 insertions(+), 11 deletions(-)
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 6736cfe749..25b2ff9d03 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -646,7 +646,7 @@ static void CreateEndOfRecoveryRecord(void);
static void CheckPointGuts(XLogRecPtr checkPointRedo, int flags);
static void KeepLogSeg(XLogRecPtr recptr, XLogSegNo *logSegNo);
-static bool XLogCheckBuffer(XLogRecData *rdata, bool doPageWrites,
+static bool XLogCheckBuffer(XLogRecData *rdata, bool holdsExclusiveLock,
XLogRecPtr *lsn, BkpBlock *bkpb);
static Buffer RestoreBackupBlockContents(XLogRecPtr lsn, BkpBlock bkpb,
char *blk, bool get_cleanup_lock, bool keep_buffer);
@@ -822,7 +822,7 @@ begin:;
{
/* OK, put it in this slot */
dtbuf[i] = rdt->buffer;
- if (XLogCheckBuffer(rdt, doPageWrites,
+ if (doPageWrites && XLogCheckBuffer(rdt, true,
&(dtbuf_lsn[i]), &(dtbuf_xlg[i])))
{
dtbuf_bkp[i] = true;
@@ -1243,7 +1243,7 @@ begin:;
* save the buffer's LSN at *lsn.
*/
static bool
-XLogCheckBuffer(XLogRecData *rdata, bool doPageWrites,
+XLogCheckBuffer(XLogRecData *rdata, bool holdsExclusiveLock,
XLogRecPtr *lsn, BkpBlock *bkpb)
{
Page page;
@@ -1251,15 +1251,17 @@ XLogCheckBuffer(XLogRecData *rdata, bool doPageWrites,
page = BufferGetPage(rdata->buffer);
/*
- * XXX We assume page LSN is first data on *every* page that can be passed
- * to XLogInsert, whether it otherwise has the standard page layout or
- * not. We don't need the buffer header lock for PageGetLSN because we
- * have exclusive lock on the page and/or the relation.
+ * We assume page LSN is first data on *every* page that can be passed
+ * to XLogInsert, whether it has the standard page layout or not. We
+ * don't need to take the buffer header lock for PageGetLSN if we hold
+ * an exclusive lock on the page and/or the relation.
*/
- *lsn = BufferGetLSNAtomic(rdata->buffer);
+ if (holdsExclusiveLock)
+ *lsn = PageGetLSN(page);
+ else
+ *lsn = BufferGetLSNAtomic(rdata->buffer);
- if (doPageWrites &&
- *lsn <= RedoRecPtr)
+ if (*lsn <= RedoRecPtr)
{
/*
* The page needs to be backed up, so set up *bkpb
@@ -7683,7 +7685,10 @@ XLogSaveBufferForHint(Buffer buffer)
rdata[0].buffer = buffer;
rdata[0].buffer_std = true;
- if (XLogCheckBuffer(rdata, true, &lsn, &bkpb))
+ /*
+ * Check buffer while not holding an exclusive lock.
+ */
+ if (XLogCheckBuffer(rdata, false, &lsn, &bkpb))
{
char copied_buffer[BLCKSZ];
char *origdata = (char *) BufferGetBlock(buffer);
--
2.40.0