From: "Ralph Mason" <ralph.mason@telogis.com>
To: "'Richard Huxton'" <dev@archonet.com>
Cc: pgsql-performance@postgresql.org
References: <011b01c798d5$141365a0$3c3a30e0$@mason@telogis.com>
	<464D6DE1.6040001@archonet.com>
In-Reply-To: <464D6DE1.6040001@archonet.com>
Subject: Re: Ever Increasing IOWAIT
Date: Mon, 21 May 2007 08:40:39 +1200
Message-ID: <005b01c79b1f$20aeb340$620c19c0$@mason@telogis.com>
MIME-Version: 1.0
Content-Type: text/plain;
	charset="windows-1250"
Content-Transfer-Encoding: quoted-printable
Thread-Index: AceZLOfOYWzCG3IgTL+sb1NK9aIOjwB8Zp8A
Content-Language: en-nz

Ralph Mason wrote:
> We have a database running on a 4 processor machine.  As time goes by=20
> the IO gets worse and worse peeking at about 200% as the machine loads =
up.
>=20
> The weird thing is that if we restart postgres it=92s fine for hours =
but=20
> over time it goes bad again.
>=20
> (CPU usage graph here HYPERLINK
> "http://www.flickr.com/photos/8347741@N02/502596262/"http://www.flickr
> .com/p hotos/8347741@N02/502596262/ )  You can clearly see where the=20
> restart happens in the IO area
>I'm assuming here we're talking about that big block of iowait at about =

>4-6am?

Actually no - that is a vacuum of the whole database to double check =
It's
not a vacuuming problem (I am sure it's not).  The restart is at at =
22:00
where you see the io drop to nothing, the database is still doing the =
same
work.

>>I take it vmstat/iostat show a corresponding increase in disk activity =

>>at that time.

I didn't know you could have IO/wait without disk activity - I will =
check
that out.=20

>>The question is - what?
>>Does the number of PG processes increase at that time? If that's not=20
>>intentional then you might need to see what your applications are up =
to.

No the number of connections is stable and the jobs they do stays the =
same,
just this deteriorating of i/o wait over time.

>>Do you have a vacuum/backup scheduled for that time? Do you have some=20
>>other process doing a lot of file I/O at that time?

> This is Postgres  8.1.4 64bit.

>You'll want to upgrade to the latest patch release - you're missing 5=20
>lots of bug-fixes there.

Thanks - will try that.


--=20
Internal Virus Database is out-of-date.
Checked by AVG Free Edition.
Version: 7.5.432 / Virus Database: 268.15.9/573 - Release Date: =
5/12/2006
4:07 p.m.
=20