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Date: Thu, 22 Feb 2007 10:12:42 +1300
From: Mark Kirkwood <markir@paradise.net.nz>
Subject: Re: Postgres performance Linux vs FreeBSD
In-reply-to: <45DC1786.80504@polok.pl>
To: =?ISO-8859-1?Q?Jacek_Zar=EAba?= <asthma@polok.pl>
Cc: pgsql-performance@postgresql.org
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Jacek Zaręba wrote:
> Hello, I've set up 2 identical machines, hp server 1ghz p3,
> 768mb ram, 18gb scsi3 drive. On the first one I've installed
> Debian/GNU 4.0 Linux, on the second FreeBSD 6.2. On both
> machines I've installed Postgresql 8.2.3 from sources.
> Now the point :)) According to my tests postgres on Linux
> box run much faster then on FreeBSD, here are my results:
> 

With respect to 'select count(*) from ...' being slower on FreeBSD, 
there are a number of things to try to make FreeBSD faster for this sort 
of query. Two I'm currently using are:

- setting sysctl vfs.read_max to 16 or 32
- rebuilding the relevant filesystem with 32K blocks and 4K frags

I have two (almost) identical systems - one running Gentoo, one running 
FreeBSD 6.2. With the indicated changes the FreeBSD system performs 
pretty much the same as the Gentoo one.

With respect to the 'explain analyze' times, FreeBSD has a more accurate 
and more expensive gettimeofday call - which hammers its 'explain 
analyze' times compared to Linux.

Cheers

Mark