Re: PostgreSQL as a local in-memory cache - Mailing list pgsql-performance

From Bruce Momjian
Subject Re: PostgreSQL as a local in-memory cache
Date
Msg-id 201006301545.o5UFjdQ07340@momjian.us
Whole thread Raw
In response to Re: PostgreSQL as a local in-memory cache  (Brad Nicholson)
List pgsql-performance
Brad Nicholson wrote:
> > > > Ah, very good point. ?I have added a C comment to clarify why this is
> > > > the current behavior; ?attached and applied.
> > > >
> > > > --
> > > > ?Bruce Momjian ?<> ? ? ? ?http://momjian.us
> > > > ?EnterpriseDB ? ? ? ? ? ? ? ? ? ? ? ? ? ? http://enterprisedb.com
> > >
> > >
> > > Though has anybody seen a behaviour where synchronous_commit=off is
> > > slower than synchronous_commit=on  ? Again there are two cases here
> > > one with O_* flag and other with f*sync flags. But I had seen that
> > > behavior with PostgreSQL 9.0 beta(2 I think) though havent really
> > > investigated it much yet .. (though now I dont remember which
> > > wal_sync_method flag) . Just curious if anybody has seen that
> > > behavior..
> >
> > I have trouble believing how synchronous_commit=off could be slower than
> > 'on'.
> >
>
> I wonder if it could be contention on wal buffers?
>
> Say I've turned synchronous_commit off, I drive enough traffic fill up
> my wal_buffers.  I assume that we would have to start writing buffers
> down to disk before allocating to the new process.

Uh, good question.  I know this report showed ynchronous_commit=off as
faster than 'on':

    http://archives.postgresql.org/pgsql-performance/2010-06/msg00277.php

--
  Bruce Momjian  <>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + None of us is going to be here forever. +

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