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Re: Usage up to 50% CPU

From: Shane Ambler <pgsql(at)Sheeky(dot)Biz>
To: Magnus Hagander <magnus(at)hagander(dot)net>
Cc: Andres Retzlaff <andres_retzlaff(at)hotmail(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Usage up to 50% CPU
Date: 2007-04-27 09:53:41
Message-ID: 4631C825.9000705@Sheeky.Biz (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
Magnus Hagander wrote:
> On Fri, Apr 27, 2007 at 08:10:48AM +0000, Andres Retzlaff wrote:
>> Hi Magnus,
>> in this case each CPU goes up to 50%, giveing me 50% total usage. I was 
>> specting as you say 1 query 100% cpu.
>> Any ideas?
> No. 1 query will only use 100% of *one* CPU, which means 50% total usage.
> You need at least one query per CPU to reach full 100% of the whole system.
> (Actually, you can get slightly above 50% since the query will run on one
> CPU and the OS and autovacuum and bgwriter can run on the other. But it's
> marginally)
> //Magnus

I would think that as you are sitting and watching the cpu usage, your 
query would seem to taking a while to run, leading me to wonder if you 
are getting a full table scan that is causing pg to wait for disk response?

Or are you running a long list of steps that take a while?


Shane Ambler

Get Sheeky @ http://Sheeky.Biz

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