From: Mark Kirkwood <markir@paradise.net.nz>
To: Jim C. Nasby <jnasby@pervasive.com>
Cc: Charles Sprickman <spork@bway.net>
Cc: pgsql-performance@postgresql.org
Subject: Re: SAN/NAS options
Date: Sat, 17 Dec 2005 11:49:55 +1300
Message-ID: <43A34493.4020204@paradise.net.nz> (raw)
In-Reply-To: <20051216221801.GT53809@pervasive.com>
References: <Pine.OSX.4.61.0512140155590.282@office-dhcp-18.bway.net>
<439FC9B8.8020709@paradise.net.nz>
<20051216221801.GT53809@pervasive.com>
Jim C. Nasby wrote:
> On Wed, Dec 14, 2005 at 08:28:56PM +1300, Mark Kirkwood wrote:
>
>>Another interesting thing to try is rebuilding the database ufs
>>filesystem(s) with 32K blocks and 4K frags (as opposed to 8K/1K or
>>16K/2K - can't recall the default on 4.x). I found this to give a factor
>>of 2 speedup on random disk access (specifically queries doing indexed
>>joins).
>
>
> Even if you're doing a lot of random IO? I would think that random IO
> would perform better if you use smaller (8K) blocks, since there's less
> data being read in and then just thrown away that way.
>
>
Yeah, that's what I would have expected too! but the particular queries
I tested do a ton of random IO (correlation of 0.013 on the join column
for the big table). I did wonder if the gain has something to do with
the underlying RAID stripe size (64K or 256K in my case), as I have only
tested the 32K vs 8K/16K on RAIDed systems.
I guess for a system where the number of concurrent users give rise to
memory pressure, it will cause more thrashing of the file buffer cache,
much could be a net loss.
Still worth trying out I think, you will know soon enough if it is a win
or lose!
Note that I did *not* alter Postgres page/block size (BLCKSZ) from 8K,
so no dump/reload is required to test this out.
cheers
Mark
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-performance@postgresql.org
Cc: markir@paradise.net.nz, jnasby@pervasive.com, spork@bway.net
Subject: Re: SAN/NAS options
In-Reply-To: <43A34493.4020204@paradise.net.nz>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox