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Re: Hardware/OS recommendations for large databases (

From: Mark Kirkwood <markir(at)paradise(dot)net(dot)nz>
To: Luke Lonergan <llonergan(at)greenplum(dot)com>
Cc: stange(at)rentec(dot)com, Greg Stark <gsstark(at)mit(dot)edu>, Dave Cramer <pg(at)fastcrypt(dot)com>, Joshua Marsh <icub3d(at)gmail(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Hardware/OS recommendations for large databases (
Date: 2005-11-24 09:26:44
Message-ID: 43858754.4020300@paradise.net.nz (view raw or flat)
Thread:
Lists: pgsql-performance
Luke Lonergan wrote:
> Mark,
> 
> 
>>>Time: 197870.105 ms
>>
>>So 198 seconds is the uncached read time with count (Just for clarity,
>>did you clear the Pg and filesystem caches or unmount / remount the
>>filesystem?)
> 
> 
> Nope - the longer time is due to the "second write" known issue with
> Postgres - it writes the data to the table, but all of the pages are marked
> dirty?  So, always on the first scan after loading they are written again.
> This is clear as you watch vmstat - the pattern on the first seq scan is
> half read / half write.
>

Ah - indeed - first access after a COPY no? I should have thought of 
that, sorry!


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