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From: Greg Smith <greg@2ndquadrant.com>
To: Scott Marlowe <scott.marlowe@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: david@lang.hm, Vitalii Tymchyshyn <tivv00@gmail.com>
Cc: Kenneth Marshall <ktm@rice.edu>
Cc: Jon Nelson <jnelson+pgsql@jamponi.net>
Cc: Andrew Dunstan <andrew@dunslane.net>
Cc: Bruce Momjian <bruce@momjian.us>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Craig Ringer <craig@postnewspapers.com.au>
Cc: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: [HACKERS] Slow count(*) again...
Date: Sat, 05 Feb 2011 03:49:05 -0500
Message-ID: <4D4D0F01.6070407@2ndquadrant.com> (raw)
In-Reply-To: <AANLkTikKTc2GPm87Liztk3UTdRY+_THquaaW3qoMe2+d@mail.gmail.com>
References: <AANLkTiknZi97dDwm7sHqy0EL7tpNEP9sY5uPV6AN+q=u@mail.gmail.com>
	<4D499E55.4020107@vmsinfo.com>
	<AANLkTimo2J-BagObs_V1bGaHOO9qL+kTF6s6-wZ=M3KW@mail.gmail.com>
	<AANLkTin7A_Q=Yc9Wf_5=POp2mVqmaiwqUDsFMLG68H45@mail.gmail.com>
	<4D4A7B69.2020704@gmail.com>
	<alpine.DEB.2.00.1102030208440.8162@asgard.lang.hm>
	<AANLkTi=Thet0VZ-X6b7tek+iSLVkE27JjiKrB5D8U0Jd@mail.gmail.com>
	<alpine.DEB.2.00.1102031243190.10088@asgard.lang.hm>
	<AANLkTikmChsPODbUD4V-gQ8k2yYvvjJY6b9K_29+k7nu@mail.gmail.com>
	<alpine.DEB.2.00.1102031637480.30983@asgard.lang.hm>
	<20110204143315.GA1261@aart.is.rice.edu>
	<4D4C0F66.1080507@gmail.com>
	<alpine.DEB.2.00.1102042142571.8162@asgard.lang.hm>
	<AANLkTi=EkCUkQs9VTtW4aOBNNNV0gi8jYZhNgdHuFTKM@mail.gmail.com>
	<AANLkTikKTc2GPm87Liztk3UTdRY+_THquaaW3qoMe2+d@mail.gmail.com>

Scott Marlowe wrote:
> With a 24 drive RAID-10 array that can read at ~1GB/s I am almost
> always CPU bound during copies.  This isn't wholly bad as it leaves
> spare IO for the rest of the machine so regular work carries on just
> fine.
>   

And you don't need nearly that much I/O bandwidth to reach that point.  
I've hit being CPU bound on COPY...FROM on systems with far less drives 
than 24.

-- 
Greg Smith   2ndQuadrant US    greg@2ndQuadrant.com   Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support  www.2ndQuadrant.us
"PostgreSQL 9.0 High Performance": http://www.2ndQuadrant.com/books




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