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From: Jesper Krogh <jesper@krogh.cc>
To: Scott Carey <scott@richrelevance.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Mladen Gogala <mladen.gogala@vmsinfo.com>
Cc: david@lang.hm <david@lang.hm>
Cc: Craig Ringer <craig@postnewspapers.com.au>
Cc: Vitalii Tymchyshyn <tivv00@gmail.com>
Cc: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: Slow count(*) again...
Date: Thu, 21 Oct 2010 20:13:24 +0200
Message-ID: <4CC082C4.4070704@krogh.cc> (raw)
In-Reply-To: <B54FDA83-1DBD-4313-AF44-EF53F3EB85D4@richrelevance.com>
References: <201010091626.18636.neil.whelchel@gmail.com>
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	<4CB4A749.3080705@krogh.cc>
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	<B54FDA83-1DBD-4313-AF44-EF53F3EB85D4@richrelevance.com>

On 2010-10-21 06:47, Scott Carey wrote:
>  On a wimpy disk, I/O bound for sure.   But my disks go 1000MB/sec.
>  No query can go fast enough for them.  The best I've gotten is
>  800MB/sec, on a wide row (average 800 bytes).  Most tables go
>  300MB/sec or so.  And with 72GB of RAM, many scans are in-memory
>  anyway.

Is it cpu or io bound while doing it?

Can you scan it faster using time cat relation-oid.* > /dev/null

>  A single SSD with supercapacitor will go about 500MB/sec by itself
>  next spring.   I will easily be able to build a system with 2GB/sec
>  I/O for under $10k.

What filesystem are you using? Readahead?
Can you try to check the filesystemfragmentation of the table using filefrag?

-- 
Jesper

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