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Re: LWLock Queue Jumping

From: Stefan Kaltenbrunner <stefan(at)kaltenbrunner(dot)cc>
To: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
Cc: Greg Stark <gsstark(at)mit(dot)edu>, Simon Riggs <simon(at)2ndquadrant(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: LWLock Queue Jumping
Date: 2009-08-30 09:48:47
Message-ID: 4A9A4AFF.8020605@kaltenbrunner.cc (view raw or flat)
Thread:
Lists: pgsql-hackers
Heikki Linnakangas wrote:
> Greg Stark wrote:
>> On Fri, Aug 28, 2009 at 8:07 PM, Simon Riggs<simon(at)2ndquadrant(dot)com> wrote:
>>> WALInsertLock is heavily contended and likely always will be even if we
>>> apply some of the planned fixes.
>> I've lost any earlier messages, could you resend the raw data on which
>> this is based?
> 
> I don't have any pointers right now, but WALInsertLock does often show
> up as a bottleneck in write-intensive benchmarks.

yeah I recently ran accross that issue with testing concurrent COPY 
performance:

http://www.kaltenbrunner.cc/blog/index.php?/archives/27-Benchmarking-8.4-Chapter-2bulk-loading.html
discussed here:

http://archives.postgresql.org/pgsql-hackers/2009-06/msg01019.php


and (iirc) also here:

http://archives.postgresql.org/pgsql-hackers/2009-06/msg01133.php


however the general issue is easily visible in almost any write 
intensive concurrent workload on a fast IO subsystem(ie 
pgbench,sysbench,...).


Stefan

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