Re: Defaulting wal_sync_method to fdatasync on Linux for 9.1? - Mailing list pgsql-performance

On Wednesday 17 November 2010 02:04:28 Tom Lane wrote:
> Andres Freund <andres@anarazel.de> writes:
> > On Wednesday 17 November 2010 01:51:28 Tom Lane wrote:
> >> Well, there's a forced fsync after writing the last page of an xlog
> >> file, but I don't believe that proves that more than 16MB of xlog
> >> buffers is useless.  Other processes could still be busy filling the
> >> buffers.
> >
> > Maybe I am missing something, but I think the relevant
> > AdvanceXLInsertBuffer() is currently called with WALInsertLock held?
>
> The fsync is associated with the write, which is not done with insert
> lock held.  We're not quite that dumb.
Ah, I see. The XLogWrite in AdvanceXLInsertBuffer is only happening if the head
of the buffer gets to the tail - which is more likely if the wal buffers are
small...

Andres