From: | Greg Smith <gsmith(at)gregsmith(dot)com> |
---|---|
To: | |
Cc: | pgsql-performance(at)postgresql(dot)org |
Subject: | Re: big database performance |
Date: | 2008-01-09 18:44:34 |
Message-ID: | Pine.GSO.4.64.0801091329330.13584@westnet.com |
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Thread: | |
Lists: | pgsql-performance |
On Wed, 9 Jan 2008, Guillaume Smet wrote:
> On Jan 9, 2008 9:27 AM, Joshua D. Drake <jd(at)commandprompt(dot)com> wrote:
>> wal_sync_method = open_sync
>
> Do you recommend it in every situation or just because data are on a
> SAN? Do you have any numbers/real cases explaining this choice.
Sync writes are faster on Linux in every case I've ever tried, compared to
the default config that does a write followed by a sync. With regular
discs they're just a little faster. On some SAN configurations, they're
enormously faster, because the SANs are often optimized to handle
syncronous writes far more efficiently than write/sync ones. This is
mainly because Oracle does its writes that way, so if you want good Oracle
performance you have to handle sync writes well.
I have something on this topic I keep meaning to publish, but I got
spooked about the potential to have silent problems or crashes when using
open_sync due to a Linux kernel issue reported here:
http://archives.postgresql.org/pgsql-hackers/2007-10/msg01310.php
Certainly with that report floating out there I'd only recommend open_sync
to people who are putting plenty of time into testing their database is
robust under load with that configuration before deploying it; I sure
wouldn't just make that changes on a production system just to see if it's
faster.
--
* Greg Smith gsmith(at)gregsmith(dot)com http://www.gregsmith.com Baltimore, MD
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