Message-ID: <454A0DD3.2050104@alteeve.com>
Date: Thu, 02 Nov 2006 10:25:07 -0500
From: Madison Kelly <linux@alteeve.com>
User-Agent: Thunderbird 1.5.0.7 (X11/20060909)
MIME-Version: 1.0
To: Scott Marlowe <smarlowe@g2switchworks.com>
CC: pgsql-performance@postgresql.org
Subject: Re: Setting "nice" values
References: <454A0B69.9070000@alteeve.com>
	<1162480836.28047.20.camel@state.g2switchworks.com>
In-Reply-To: <1162480836.28047.20.camel@state.g2switchworks.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit

Scott Marlowe wrote:
> 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.

Will the priority of the script pass down to the pgsql queries it calls? 
I figured (likely incorrectly) that because the queries were executed by 
the psql server the queries ran with the server's priority. If this 
isn't the case, then perfect. :)

Thanks for the tip, too, it's something I will try.

Madi