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Re: AIX slow buffer reads

From: André Volpato <andre(dot)volpato(at)ecomtecnologia(dot)com(dot)br>
To: Greg Smith <greg(at)2ndquadrant(dot)com>
Cc: Brad Nicholson <bnichols(at)ca(dot)afilias(dot)info>, pgsql-performance(at)postgresql(dot)org
Subject: Re: AIX slow buffer reads
Date: 2010-10-28 12:33:07
Message-ID: 647835811.10922.1288269187954.JavaMail.root@zimbra01a (view raw or flat)
Thread:
Lists: pgsql-performance
----- Mensagem original -----
| André Volpato wrote:
| > |
| > | If it is being spent in the bitmap index scan, try setting
| > | effective_io_concurrency to 0 for Linux, and see what effect that
| > | has.
| >
| > I disabled effective_io_concurrency at AIX but it made no changes on
| > bitmap index times.
| >
| 
| Brad's point is that it probably doesn't do anything at all on AIX,
| and
| is already disabled accordingly. But on Linux, it is doing something,
| and that might be contributing to why it's executing so much better on
| that platform. If you disable that parameter on your Debian box, that
| should give you an idea whether that particular speed-up is a major
| component to the difference you're seeing or not.


Here´s new explains based on Debian box:

(1) effective_io_concurrency = 5
# /etc/init.d/postgresql stop
# echo 3 > /proc/sys/vm/drop_caches
# /etc/init.d/postgresql start

http://explain.depesz.com/s/br

(2) effective_io_concurrency = 0
# /etc/init.d/postgresql stop
# echo 3 > /proc/sys/vm/drop_caches
# /etc/init.d/postgresql start

http://explain.depesz.com/s/3A0

BitmapAnd really gets improved a little bit in (1), but Bitmap index scans got a lot worse.


| --
| Greg Smith 2ndQuadrant US greg(at)2ndQuadrant(dot)com Baltimore, MD
| PostgreSQL Training, Services and Support www.2ndQuadrant.us
| "PostgreSQL 9.0 High Performance": http://www.2ndQuadrant.com/books

[]´s, Andre Volpato

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