From: Luke Lonergan <llonergan@greenplum.com>
To: Hannu Krosing <hannu@skype.net>
To: Josh Berkus <josh@agliodbs.com>
Cc: Jeffrey W. Baker <jwbaker@acm.org>
Cc: pgsql-hackers@postgresql.org, "Michael Stone" <mstone+postgres@mathom.us>
Cc: pgsql-performance@postgresql.org
Subject: Re: [HACKERS] A Better External Sort?
Date: Mon, 03 Oct 2005 14:52:27 -0700
Message-ID: <BF66F62B.108A0%llonergan@greenplum.com> (raw)
In-Reply-To: <1128375790.5882.18.camel@fuji.krosing.net>
Hannu,
On 10/3/05 2:43 PM, "Hannu Krosing" <hannu@skype.net> wrote:
> Just FYI, I run a count(*) on a 15.6GB table on a lightly loaded db and
> it run in 163 sec. (Dual opteron 2.6GHz, 6GB RAM, 6 x 74GB 15k disks in
> RAID10, reiserfs). A little less than 100MB sec.
This confirms our findings - sequential scan is CPU limited at about 120MB/s
per single threaded executor. This is too slow for fast file systems like
we're discussing here.
Bizgres MPP gets 250MB/s by running multiple scanners, but we still chew up
unnecessary amounts of CPU.
> After this I ran count(*) over a 2.4GB file from another tablespace on
> another device (4x142GB 10k disks in RAID10) and it run 22.5 sec on
> first run and 12.5 on second.
You're getting caching effects here.
- Luke
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To: pgsql-performance@postgresql.org
Cc: llonergan@greenplum.com, hannu@skype.net, josh@agliodbs.com, jwbaker@acm.org, mstone+postgres@mathom.us
Subject: Re: [HACKERS] A Better External Sort?
In-Reply-To: <BF66F62B.108A0%llonergan@greenplum.com>
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