From: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
---|---|
To: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
Cc: | josh(at)agliodbs(dot)com, Hans-Jürgen Schönig <postgres(at)cybertec(dot)at>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: commit_delay, siblings |
Date: | 2005-06-29 12:03:19 |
Message-ID: | 200506291203.j5TC3J202105@candle.pha.pa.us |
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Lists: | pgsql-hackers |
Simon Riggs wrote:
> On Wed, 2005-06-22 at 11:11 -0700, Josh Berkus wrote:
> > Hans, Tom,
> >
> > > We have done extensive testing some time ago.
> > > We could not see any difference on any platform we have tested (AIX,
> > > Linux, Solaris). I don't think that there is one at all - at least not
> > > on common systems.
> >
> > Keen then. Any objections to removing the GUC? We desperately need means
> > to cut down on GUC options.
>
> Group commit is a well-documented technique for improving performance,
> but the gains only show themselves on very busy systems. It is possible
> in earlier testing any apparent value was actually hidden by the
> BufMgrLock issues we have now resolved in 8.1. We now see XLogInsert as
> being very nearly the highest routine on the oprofile. That tells me
> that it could now be time for group commit to show us some value, if any
> exists.
>
> DB2 and Berkeley-DB use group commit, while other rdbms use log writer
> processes which effectively provide the same thing. It would surprise me
> if we were unable to make use of such a technique, and worry me too.
>
> I would ask that we hold off on their execution, at least for the
> complete 8.1 beta performance test cycle. We may yet see gains albeit,
> as Tom points out, that benefit may only be possible on only some
> platforms.
Interesting. I didn't know other databases used group commits. Your
idea of keeping it for the 8.1 testing cycle has merit.
--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 359-1001
+ If your life is a hard drive, | 13 Roberts Road
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