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Re: Stats collector performance improvement

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Michael Fuhr <mike(at)fuhr(dot)org>, Merlin Moncure <merlin(dot)moncure(at)rcsonline(dot)com>, Carlos Benkendorf <carlosbenkendorf(at)yahoo(dot)com(dot)br>, PostgreSQL-patches <pgsql-patches(at)postgresql(dot)org>
Subject: Re: Stats collector performance improvement
Date: 2006-01-02 19:13:47
Message-ID: 200601021913.k02JDlh26741@candle.pha.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-patchespgsql-performance
Tom Lane wrote:
> Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> > I found if I put a pg_usleep(100) in the buffer process the backend
> > speed was good, but packets were lost.  What I found worked well was to
> > do multiple recv() calls in a loop.  The previous code did a select(),
> > then perhaps a recv() and pipe write() based on the results of the
> > select().  This caused many small packets to be written to the pipe and
> > the pipe write overhead seems fairly large.  The best fix I found was to
> > loop over the recv() call at most 25 times, collecting a group of
> > packets that can then be sent to the collector in one pipe write.  The
> > recv() socket is non-blocking, so a zero return indicates there are no
> > more packets available.  Patch attached.
> 
> This seems incredibly OS-specific.  How many platforms did you test it
> on?

Only mine.  I am posting the patch so others can test it, of course.

> A more serious objection is that it will cause the stats machinery to
> work very poorly if there isn't a steady stream of incoming messages.
> You can't just sit on 24 messages until the 25th one arrives next week.

You wouldn't.  It exits out of the loop on a not found, checks the pipe
write descriptor, and writes on it.

-- 
  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
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

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