Re: Checkpointer write combining

Hi all,

Based on the ongoing discussions on Checkpointer Write Combining [1] and the last patch v11 discussed in forum, I have re-implemented the logic for CleanVictimBuffer() and BufferNeedsWALFlush() with a few changes:

static void
CleanVictimBuffer(BufferDesc *bufdesc, bool from_ring, IOContext io_context)
{
XLogRecPtr max_lsn = InvalidXLogRecPtr;
LWLock *content_lock;
content_lock = BufHdrGetContentLock(bufdesc);
LWLockAcquire(content_lock, LW_SHARED);
if (!PrepareFlushBuffer(bufdesc, &max_lsn))
{
LWLockRelease(content_lock);
return;
}
LWLockRelease(content_lock);
LWLockAcquire(content_lock, LW_EXCLUSIVE);
if (!PrepareFlushBuffer(bufdesc, &max_lsn))
{
LWLockRelease(content_lock);
return;
}
BufferSetStateWriteInProgress(bufdesc);
LWLockRelease(content_lock);
RecordBufferForBatch(bufdesc, max_lsn);
}

Here I added some extra safety checks and early-exit handling, making sure the function returns cleanly when a buffer no longer needs writing and ensuring locks are handled correctly.

static bool
BufferNeedsWALFlush(BufferDesc *bufdesc, XLogRecPtr *lsn)
{
uint32 buf_state;
buf_state = LockBufHdr(bufdesc);
if (buf_state & BM_PERMANENT)
 *lsn = BufferGetLSN(bufdesc);
else
 *lsn = InvalidXLogRecPtr;
UnlockBufHdr(bufdesc);
if (!(*lsn != InvalidXLogRecPtr))
return false;
return XLogNeedsFlush(*lsn);
}