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Re: Hardware/OS recommendations for large databases (

From: William Yu <wyu(at)talisys(dot)com>
To: pgsql-performance(at)postgresql(dot)org
Subject: Re: Hardware/OS recommendations for large databases (
Date: 2005-11-20 12:55:14
Message-ID: dlprnd$25d0$ (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
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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Subject: Re: Hardware/OS recommendations for large databases (
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