Re: High load and iowait but no disk access

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Rémy Beaumont <remyb(at)medrium(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: High load and iowait but no disk access
Date: 2005-08-30 16:29:02
Message-ID: 22550.1125419342@sss.pgh.pa.us
Views: Raw Message | Whole Thread | Download mbox | Resend email
Thread:
Lists: pgsql-performance

=?ISO-8859-1?Q?R=E9my_Beaumont?= <remyb(at)medrium(dot)com> writes:
> On 30-Aug-05, at 12:15, Tom Lane wrote:
>> I know zip about NetApps, but doesn't the 8th column indicate pretty
>> steady disk reads?

> Yes, but they are very low.

Sure, but that's more or less what you'd expect if the thing is randomly
seeking all over the disk :-(. Just because it's a NetApp doesn't mean
it's got zero seek time.

You did not say what sort of query this is, but I gather that it's doing
an indexscan on a table that is not at all in index order. Possible
solutions involve reverting to a seqscan (have you forced the planner to
choose an indexscan here, either directly or by lowering random_page_cost?)
or CLUSTERing the table by the index (which would need to be repeated
periodically, so it's not a great answer).

regards, tom lane

In response to

Responses

Browse pgsql-performance by date

  From Date Subject
Next Message Jeffrey W. Baker 2005-08-30 16:39:17 Re: Observation about db response time
Previous Message Michael Stone 2005-08-30 16:25:25 Re: High load and iowait but no disk access