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Re: PostgreSQL as a local in-memory cache

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Brad Nicholson <bnichols(at)ca(dot)afilias(dot)info>
Cc: Jignesh Shah <jkshah(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Robert Haas <robertmhaas(at)gmail(dot)com>, Dimitri Fontaine <dfontaine(at)hi-media(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, postgres performance list <pgsql-performance(at)postgresql(dot)org>
Subject: Re: PostgreSQL as a local in-memory cache
Date: 2010-06-30 15:45:39
Message-ID: 201006301545.o5UFjdQ07340@momjian.us (view raw or flat)
Thread:
Lists: 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 ?<bruce(at)momjian(dot)us> ? ? ? ?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  <bruce(at)momjian(dot)us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

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

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Subject: Re: PostgreSQL as a local in-memory cache
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