http://www.postgresql.org/docs/current/static/wal-async-commit.html
"
the server waits for the transaction's WAL records to be flushed to permanent storage before returning a success indication to the client."
I think with fynch=off, whether WAL gets written to disk or not is still controlled by synchronous_commit parameter. guessing here...
> Date: Wed, 16 Jun 2010 12:19:20 -0700
> Subject: Re: [PERFORM] PostgreSQL as a local in-memory cache
> From: jgardner@jonathangardner.net
> To: josh@agliodbs.com
> CC: pgsql-performance@postgresql.org
>
> On Wed, Jun 16, 2010 at 12:00 PM, Josh Berkus <josh@agliodbs.com> wrote:
> >
> >> * fsync=off => 5,100
> >> * fsync=off and synchronous_commit=off => 5,500
> >
> > Now, this *is* interesting ... why should synch_commit make a difference
> > if fsync is off?
> >
> > Anyone have any ideas?
> >
>
> I may have stumbled upon this by my ignorance, but I thought I read
> that synchronous_commit controlled whether it tries to line up commits
> or has a more free-for-all that may cause some intermediate weirdness.
>
> --
> Jonathan Gardner
> jgardner@jonathangardner.net
>
> --
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