On Thu, Jul 14, 2011 at 9:57 AM, Fujii Masao <masao.fujii@gmail.com> wrote:
> Currently walwriter might write out the WAL before a transaction commits.
> IOW, walwriter tries to write out the WAL in wal_buffers in every wakeups.
> This might be useful for long transaction which generates lots of WAL
> records before commit. So we should call SetLatch() in XLogInsert() instead
> of RecordTransactionCommit()? Though I'm not sure how much walwriter
> improves the performance of synchronous commit case..
Yeh, we did previously have a heuristic to write out the WAL when it
was more than half full. Not sure I want to put exactly that code back
into such a busy code path.
I suggest that we set latch every time the wal buffers wrap.
So at the bottom of AdvanceXLInsertBuffer(), if nextidx == 0 then
SetLatch on the WALWriter.
That's a simple test and we only check it if we're switch WAL buffer page.
--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services