Subject: Re: Setting "nice" values
From: Scott Marlowe <smarlowe@g2switchworks.com>
To: Madison Kelly <linux@alteeve.com>
Cc: pgsql-performance@postgresql.org
In-Reply-To: <454A0B69.9070000@alteeve.com>
References: <454A0B69.9070000@alteeve.com>
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Date: Thu, 02 Nov 2006 09:20:36 -0600

On Thu, 2006-11-02 at 09:14, Madison Kelly wrote:
> Hi all,
> 
>    I've got a script (perl, in case it matters) that I need to run once
> a month to prepare statements. This script queries and updates the
> database a *lot*. I am not concerned with the performance of the SQL
> calls so much as I am about the impact it has on the server's load.
> 
>    Is there a way to limit queries speed (ie: set a low 'nice' value on
> a query)? This might be an odd question, or I could be asking the
> question the wrong way, but hopefully you the idea. :)

While you can safely set the priority lower on the calling perl script,
setting db backend priorities lower can result in problems caused by
"priority inversion"  Look up that phrase on the pgsql admin, perform,
general, or hackers lists for an explanation, or go here:

http://en.wikipedia.org/wiki/Priority_inversion

I have a simple script that grabs raw data from an oracle db and shoves
it into a postgresql database for reporting purposes.  Every 100 rows I
put into postgresql, I usleep 10 or so and the load caused by that
script on both systems is minimal.  You might try something like that.