Date: Thu, 28 Oct 2010 10:33:07 -0200 (BRST)
From: =?utf-8?Q?Andr=C3=A9_Volpato?= <andre.volpato@ecomtecnologia.com.br>
To: Greg Smith <greg@2ndquadrant.com>
Cc: Brad Nicholson <bnichols@ca.afilias.info>,
 pgsql-performance@postgresql.org
Message-ID: <647835811.10922.1288269187954.JavaMail.root@zimbra01a>
In-Reply-To: <4CC87C69.5070301@2ndquadrant.com>
Subject: Re: AIX slow buffer reads
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----- Mensagem original -----
| Andr=C3=A9 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.
| >
|=20
| 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=C2=B4s new explains based on Debian box:

(1) effective_io_concurrency =3D 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 =3D 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@2ndQuadrant.com Baltimore, MD
| PostgreSQL Training, Services and Support www.2ndQuadrant.us
| "PostgreSQL 9.0 High Performance": http://www.2ndQuadrant.com/books

[]=C2=B4s, Andre Volpato