Re: Async Commit, v21 (now: v22)

On Tue, 2007-07-24 at 10:01 -0400, Tom Lane wrote:
> Gregory Stark <stark(at)enterprisedb(dot)com> writes:
> > Without async commits? Do we really want the walwriter doing the
> > majority of the wal-flushing work for normal commits? It seems like
> > that's not going to be any advantage over just having some random
> > backend do the commit.
>
> Sure: the advantage is that the backends (ie, user query processing)
> don't get blocked on fsync's. This is not really different from the
> rationale for having the bgwriter.

Let's measure things and set the defaults accordingly.

> It's probably most useful for large
> transactions, which up to now generally had to stop and flush the WAL
> buffers every few pages worth of WAL output.

That should be a reasonable gain from avoiding CPU/disk flip-flopping,
but we are still CPU bound on COPY. Will measure.

--
Simon Riggs
EnterpriseDB http://www.enterprisedb.com