From: Laurent Laborde <kerdezixe@gmail.com>
To: Ivan Voras <ivoras@freebsd.org>
Cc: pgsql-performance@postgresql.org
Subject: Re: limiting performance impact of wal archiving.
Date: Tue, 10 Nov 2009 16:00:06 +0100
Message-ID: <8a1bfe660911100700l2a44f638m97ea6136b65deb21@mail.gmail.com> (raw)
In-Reply-To: <hdbrv8$p35$1@ger.gmane.org>
References: <8a1bfe660911100355l34a557ffj8244079c1fb689b5@mail.gmail.com>
<hdbrv8$p35$1@ger.gmane.org>
On Tue, Nov 10, 2009 at 3:05 PM, Ivan Voras <ivoras@freebsd.org> wrote:
> Laurent Laborde wrote:
>>
>> Hi !
>> We recently had a problem with wal archiving badly impacting the
>> performance of our postgresql master.
>
> Hmmm, do you want to say that copying 16 MB files over the network (and
> presumably you are not doing it absolutely continually - there are pauses
> between log shipping - or you wouldn't be able to use bandwidth limiting) in
> an age when desktop drives easily read 60 MB/s (and besides most of the file
> should be cached by the OS anyway) is a problem for you? Slow hardware?
>
> (or I've misunderstood the problem...)
Desktop drive can easily do 60MB/s in *sequential* read/write.
We use high performance array of 15.000rpm SAS disk on an octocore
32GB and IO is always a problem.
I explain the problem :
This server (doing wal archiving) is the master node of the
over-blog's server farm.
hundreds of GB of data, tens of millions of articles and comments,
millions of user, ...
~250 read/write sql requests per seconds for the master
~500 read sql request per slave.
Awefully random access overload our array at 10MB/s at best.
Of course, when doing sequential read it goes to +250MB/s :)
Waiting for "cheap" memory to be cheap enough to have 512Go of ram per server ;)
We tought about SSD.
But interleaved read/write kill any SSD performance and is not better
than SSD. Just more expensive with an unknown behaviour over age.
--
ker2x
sysadmin & DBA @ http://www.over-blog.com/
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To: pgsql-performance@postgresql.org
Cc: kerdezixe@gmail.com, ivoras@freebsd.org
Subject: Re: limiting performance impact of wal archiving.
In-Reply-To: <8a1bfe660911100700l2a44f638m97ea6136b65deb21@mail.gmail.com>
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