From: Greg Smith <gsmith@gregsmith.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: big database performance
Date: Wed, 9 Jan 2008 13:44:34 -0500 (EST)
Message-ID: <Pine.GSO.4.64.0801091329330.13584@westnet.com> (raw)
In-Reply-To: <1d4e0c10801090859l55b35082r5992a1bb81f1ec32@mail.gmail.com>
References: <4784835A.8070604@careerjunction.co.za>
<47848575.8000007@commandprompt.com>
<1d4e0c10801090859l55b35082r5992a1bb81f1ec32@mail.gmail.com>
On Wed, 9 Jan 2008, Guillaume Smet wrote:
> On Jan 9, 2008 9:27 AM, Joshua D. Drake <jd@commandprompt.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@gregsmith.com http://www.gregsmith.com Baltimore, MD
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To: pgsql-performance@postgresql.org
Cc: gsmith@gregsmith.com
Subject: Re: big database performance
In-Reply-To: <Pine.GSO.4.64.0801091329330.13584@westnet.com>
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