From: | Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com> |
---|---|
To: | Tomas Vondra <tv(at)fuzzy(dot)cz> |
Cc: | Ogden <lists(at)darkstatic(dot)com>, pgsql-performance(at)postgresql(dot)org |
Subject: | Re: Tuning Tips for a new Server |
Date: | 2011-08-17 19:14:26 |
Message-ID: | CAOR=d=0NAmTbYE1epENHiP0UjbivpPvzwC2z951YQBuja86z2Q@mail.gmail.com |
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Lists: | pgsql-performance |
On Wed, Aug 17, 2011 at 12:56 PM, Tomas Vondra <tv(at)fuzzy(dot)cz> wrote:
>
> I think you've mentioned the database is on 6 drives, while the other
> volume is on 2 drives, right? That makes the OS drive about 3x slower
> (just a rough estimate). But if the database drive is used heavily, it
> might help to move the xlog directory to the OS disk. See how is the db
> volume utilized and if it's fully utilized, try to move the xlog
> directory.
>
> The only way to find out is to actualy try it with your workload.
This is a very important point. I've found on most machines with
hardware caching RAID and 8 or fewer 15k SCSI drives it's just as
fast to put it all on one big RAID-10 and if necessary partition it to
put the pg_xlog on its own file system. After that depending on the
workload you might need a LOT of drives in the pg_xlog dir or just a
pair. Under normal ops many dbs will use only a tiny % of a
dedicated pg_xlog. Then something like a site indexer starts to run,
and writing heavily to the db, and the usage shoots to 100% and it's
the bottleneck.
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