Re: commit_delay, siblings

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.

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