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Re: LWLock contention: I think I understand the problem

From: Fredrik Estreen <estreen(at)algonet(dot)se>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Tatsuo Ishii <t-ishii(at)sra(dot)co(dot)jp>, pgman(at)candle(dot)pha(dot)pa(dot)us, pgsql-hackers(at)postgresql(dot)org, jwbaker(at)acm(dot)org
Subject: Re: LWLock contention: I think I understand the problem
Date: 2002-01-04 11:58:28
Message-ID: 3C3598E4.6000501@algonet.se (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-odbc
  Tom Lane wrote:

>Attached is a modification that prevents additional waiters from being
>released until the first releasee has a chance to run and acquire the
>lock.  Would you try this and see if it's better or not in your test
>cases?  It doesn't seem to help on a single CPU, but maybe on multiple
>CPUs it'll make a difference.
>
Here are some results for Linux 2.2 on a Dual PentiumPro 200MHz, SCSI 
disks and way too litte RAM
(just 128MB). I observed the loadavg. with the three different 7.2 
versions and 50 clients, without patch
the load stayed low (2-3), with patch no1 very high (12-14) and with 
patch no2 between the two others
(6-8). Any of the patches seem to be a big win with the second version 
being slightly better. I could run
benchmarks on 7.1 if that would be interesting. I used the same 
benchmark database with a
VACUUM FULL between each version of the backend tested. I also re-run 
some of the tests on the same
database after I tested all loads on the different versions, and numbers 
stayed very simmilar (difference:
 0.1-0.3 tps).

Best regrds
    Fredrik Estreen


Attachment: pgbench.txt
Description: text/plain (5.1 KB)

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