Re: Rather large LA

On Monday 05 Sep 2011 22:23:32 Scott Marlowe wrote:
> On Mon, Sep 5, 2011 at 11:24 AM, Andres Freund <andres(at)anarazel(dot)de> wrote:
> > On Monday, September 05, 2011 14:57:43 Richard Shaw wrote:
> >> Autovacuum has been disabled and set to run manually via cron during a
> >> quiet period and fsync has recently been turned off to gauge any real
> >> world performance increase, there is battery backup on the raid card
> >> providing some level of resilience.
> >
> > That doesn't help you against a failure due to fsync() off as the BBU can
> > only protect data that actually has been written to disk. Without
> > fsync=on no guarantee about that exists.
>
> Further, if you've got a bbu cache on the RAID card the gains from
> fsync=off wll be low / nonexistent.
Thats not necessarily true. If you have a mixed load of many small writes and
some parallel huge writes (especially in combination with big indexes)
fsync=off still can give you quite big performance increases. Even in the
presenence of synchronous_commit=off.

Andres