From: Josh Berkus <josh@agliodbs.com>
To: pgsql-performance@postgresql.org
Cc: Jignesh Shah <jkshah@gmail.com>
Subject: 8K recordsize bad on ZFS?
Date: Fri, 07 May 2010 17:09:45 -0700
Message-ID: <4BE4ABC9.6040106@agliodbs.com> (raw)
Jignesh, All:
Most of our Solaris users have been, I think, following Jignesh's advice
from his benchmark tests to set ZFS page size to 8K for the data zpool.
However, I've discovered that this is sometimes a serious problem for
some hardware.
For example, having the recordsize set to 8K on a Sun 4170 with 8 drives
recently gave me these appalling Bonnie++ results:
Version 1.96 ------Sequential Output------ --Sequential Input-
--Random-
Concurrency 4 -Per Chr- --Block-- -Rewrite- -Per Chr- --Block--
--Seeks--
Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP
/sec %CP
db111 24G 260044 33 62110 17 89914 15
1167 25
Latency 6549ms 4882ms 3395ms
107ms
I know that's hard to read. What it's saying is:
Seq Writes: 260mb/s combined
Seq Reads: 89mb/s combined
Read Latency: 3.3s
Best guess is that this is a result of overloading the array/drives with
commands for all those small blocks; certainly the behavior observed
(stuttering I/O, latency) is in line with that issue.
Anyway, since this is a DW-like workload, we just bumped the recordsize
up to 128K and the performance issues went away ... reads up over 300mb/s.
--
-- Josh Berkus
PostgreSQL Experts Inc.
http://www.pgexperts.com
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To: pgsql-performance@postgresql.org
Cc: josh@agliodbs.com, jkshah@gmail.com
Subject: Re: 8K recordsize bad on ZFS?
In-Reply-To: <4BE4ABC9.6040106@agliodbs.com>
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