Message-ID: <43807D31.6050008@rentec.com>
Date: Sun, 20 Nov 2005 08:42:09 -0500
From: Alan Stange <stange@rentec.com>
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To: William Yu <wyu@talisys.com>
CC: pgsql-performance@postgresql.org
Subject: Re: Hardware/OS recommendations for large databases (
References: <BFA48F15.14182%llonergan@greenplum.com>
	<437FE2E4.5040600@rentec.com> <dlprnd$25d0$1@news.hub.org>
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William Yu wrote:
> Alan Stange wrote:
>> Luke Lonergan wrote:
>>> The "aka iowait" is the problem here - iowait is not idle (otherwise it
>>> would be in the "idle" column).
>>>
>>> Iowait is time spent waiting on blocking io calls.  As another poster
>>> pointed out, you have a two CPU system, and during your scan, as 
>>
>> iowait time is idle time. Period.   This point has been debated 
>> endlessly for Solaris and other OS's as well.
>
> I'm sure the the theory is nice but here's my experience with iowait 
> just a minute ago. I run Linux/XFce as my desktop -- decided I wanted 
> to lookup some stuff in Wikipedia under Mozilla and my computer system 
> became completely unusable for nearly a minute while who knows what 
> Mozilla was doing. (Probably loading all the language packs.) I could 
> not even switch to IRC (already loaded) to chat with other people 
> while Mozilla was chewing up all my disk I/O.
>
> So I went to another computer, connected to mine remotely (slow...) 
> and checked top. 90% in the "wa" column which I assume is the iowait 
> column. It may be idle in theory but it's not a very useful idle -- 
> wasn't able to switch to any programs already running, couldn't click 
> on the XFce launchbar to run any new programs.

So, you have a sucky computer.    I'm sorry, but iowait is still idle 
time, whether you believe it or not.

-- Alan