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Skip extraneous locking in XLogCheckBuffer().

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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.
This commit is contained in:
Simon Riggs 2013-04-08 09:11:49 +01:00
parent 47c4333189
commit 5787c6730e
1 changed files with 16 additions and 11 deletions
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27
src/backend/access/transam/xlog.c
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@ -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);