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.
@@ -624,7 +624,7 @@ static bool recoveryStopsHere(XLogRecord *record, bool *includeThis);
static void CheckPointGuts(XLogRecPtr checkPointRedo, int flags);
static void Checkpoint_RecoveryPass(XLogRecPtr checkPointRedo);
-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);
@@ -960,7 +960,7 @@ 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;
@@ -1522,7 +1522,7 @@ XLogLastInsertDataLen(void)
* save the buffer's LSN at *lsn.
*/
static bool
-XLogCheckBuffer(XLogRecData *rdata, bool doPageWrites,
+XLogCheckBuffer(XLogRecData *rdata, bool holdsExclusiveLock,
XLogRecPtr *lsn, BkpBlock *bkpb)
{
PageHeader page;
@@ -1530,14 +1530,17 @@ XLogCheckBuffer(XLogRecData *rdata, bool doPageWrites,
page = (PageHeader) BufferGetBlock(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 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.
*/
+ if (holdsExclusiveLock)
+ *lsn = PageGetLSN(page);
+ else
*lsn = BufferGetLSNAtomic(rdata->buffer);
- if (doPageWrites &&
- XLByteLE(*lsn, RedoRecPtr))
+ if (XLByteLE(*lsn, RedoRecPtr))
{
/*
* The page needs to be backed up, so set up *bkpb
@@ -9593,7 +9596,10 @@ 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);
