Re: Query Performance and IOWait

From our experience it is not just a postgres issue, but all IO with the
Update 3 kernel.

We have a box with Update 3 that queries a remote postgres database(Running
RH7.3, RH3 Update2) and writes to a file on an NFS server. The update 3
box does half the work with 2-3 times the load as our update 1 and 2 boxes.
Looking at top the box is always above 90% IO Wait on the CPU. When we
downgrade the kernel to Update 2 it seems to fix the issue.

We several Update 3 boxes that run postgres locally and they all struggle
compared to the Update 2 boxes

We have tried the Fedora Core 3 with not much more success and we are going
to try the Update 4 beta kernel next week to see if it is any better.

There are several threads on the Taroon mailing list discussing the issue.

Woody

-----Original Message-----
From: Josh Berkus [mailto:josh(at)agliodbs(dot)com]
Sent: Thursday, November 18, 2004 1:34 PM
To: pgsql-performance(at)postgresql(dot)org
Cc: Woody Woodring; 'Andrew Janian'
Subject: Re: [PERFORM] Query Performance and IOWait

Woody,

> What version of Redhat are you running?   We have found running
> Enterprise Update 3 kernel kills our Dell boxes with IOWait, both NFS
> and local disk traffic.  Update 2 kernel does not seem to have the
> issue, and we are in the process of trying Update 4 beta to see if it is
better.

This is interesting; do you have more to say about it? I've been having
some
mysterious issues with RHES that I've not been able to pin down.

--
Josh Berkus
Aglio Database Solutions
San Francisco