From: Tom Lane <tgl@sss.pgh.pa.us>
To: Bruce Momjian <pgman@candle.pha.pa.us>
Cc: Michael Fuhr <mike@fuhr.org>
Cc: Merlin Moncure <merlin.moncure@rcsonline.com>
Cc: Carlos Benkendorf <carlosbenkendorf@yahoo.com.br>
Cc: PostgreSQL-patches <pgsql-patches@postgresql.org>
Subject: Re: Stats collector performance improvement
Date: Mon, 02 Jan 2006 13:45:21 -0500
Message-ID: <7838.1136227521@sss.pgh.pa.us> (raw)
In-Reply-To: <200601021840.k02Ieed21704@candle.pha.pa.us>
References: <200601021840.k02Ieed21704@candle.pha.pa.us>
Bruce Momjian <pgman@candle.pha.pa.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?
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.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, pgman@candle.pha.pa.us, mike@fuhr.org, merlin.moncure@rcsonline.com, carlosbenkendorf@yahoo.com.br, pgsql-patches@postgresql.org
Subject: Re: Stats collector performance improvement
In-Reply-To: <7838.1136227521@sss.pgh.pa.us>
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