From: William Yu <wyu@talisys.com>
To: pgsql-performance@postgresql.org
Subject: Re: Hardware/OS recommendations for large databases (
Date: Sun, 20 Nov 2005 04:55:14 -0800
Message-ID: <dlprnd$25d0$1@news.hub.org> (raw)
In-Reply-To: <437FE2E4.5040600@rentec.com>
References: <BFA48F15.14182%llonergan@greenplum.com>
<437FE2E4.5040600@rentec.com>
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.
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To: pgsql-performance@postgresql.org
Cc: wyu@talisys.com
Subject: Re: Hardware/OS recommendations for large databases (
In-Reply-To: <dlprnd$25d0$1@news.hub.org>
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