Re: Query kills machine.

From: "Magnus Naeslund(pg)" <mag-pg(at)fbab(dot)net>
To: Stef <svb(at)ucs(dot)co(dot)za>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Query kills machine.
Date: 2004-08-24 14:15:06
Message-ID: 412B4D6A.8050706@fbab.net
Views: Raw Message | Whole Thread | Download mbox | Resend email
Thread:
Lists: pgsql-performance

Stef wrote:

> Christopher Kings-Lynne mentioned :
> => sort_mem = 4096
>
> Reducing sort_mem to 4096 seems to make it run in a reasonable time
> again. Any idea why? The database does a whole lot of huge sorts
> every day, so I thought upping this parameter would help.
>
> A couple of queries do seem to run slower now that I reduced
> the sort_mem.
> The shared buffers still makes a significant difference when I
increase it.
>

Well you have to take in account that sort_mem is not the total memory
allocated for sorting but per connection and in complex expressions
serveral times that too.

So if you sort a lot it can push your operating system off the cliff and
it might start reaping things that shouldn't be reaped and start swapping.

If that happens _everything_ on that box will get slow...

Shared buffers on the other hand is only allocated once.

Regards,
Magnus

In response to

Browse pgsql-performance by date

  From Date Subject
Next Message Tom Lane 2004-08-24 15:23:31 Re: Query kills machine.
Previous Message Magnus Naeslund(t) 2004-08-24 14:08:33 Re: Query kills machine.