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Date: Wed, 17 Aug 2011 21:44:10 +0200
Subject: Re: Tuning Tips for a new Server
From: "Tomas Vondra" <tv@fuzzy.cz>
To: "Ogden" <lists@darkstatic.com>
Cc: "Scott Marlowe" <scott.marlowe@gmail.com>, "Tomas Vondra" <tv@fuzzy.cz>,
	pgsql-performance@postgresql.org
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On 17 Srpen 2011, 21:22, Ogden wrote:
>> 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.
>
> I suppose this is my confusion. Or rather I am curious about this. On my
> current production database the pg_xlog directory is 8Gb (our total
> database is 200Gb). Does this warrant a totally separate setup (and
> hardware) than PGDATA?

This is not about database size, it's about the workload - the way you're
using your database. Even a small database may produce a lot of WAL
segments, if the workload is write-heavy. So it's impossible to recommend
something except to try that on your own.

Tomas