From: Jim C. Nasby <jnasby@pervasive.com>
To: Anjan Kumar. A. <anjankumar@cse.iitb.ac.in>
Cc: pgsql-hackers@postgresql.org
Subject: Re: Please Help: PostgreSQL Query Optimizer
Date: Mon, 12 Dec 2005 14:40:03 -0600
Message-ID: <20051212204003.GY54639@pervasive.com> (raw)
In-Reply-To: <Pine.LNX.4.61.0512121833490.11179@nsl-33.cse.iitb.ac.in>
References: <Pine.LNX.4.61.0512111610320.4525@nsl-33.cse.iitb.ac.in>
<17378.1134321553@sss.pgh.pa.us>
<Pine.LNX.4.61.0512121833490.11179@nsl-33.cse.iitb.ac.in>
On Mon, Dec 12, 2005 at 06:39:42PM +0530, Anjan Kumar. A. wrote:
> Through googling, i found that Normal Disk has external data transfer rate
> of around 40MBps,
> where as Main Memory has Data transfer rate ranging from 1.6GBps to 2.8GBps.
I think 40MB/s is a burst speed. You should do some testing to verify.
In any case, PostgreSQL doesn't come close to the theoretical maximum
disk bandwidth even on a sequential scan. There's been discussion about
this on various lists in the past. For a single drive, expect something
more in the range of 4-6MB/s (depending on the drive).
More important that throughput though, is latency. Because the latency
on memory is much closer to 0 (it's not truely 0 due to L1/L2 caching),
you can serve concurrent requests a lot faster.
--
Jim C. Nasby, Sr. Engineering Consultant jnasby@pervasive.com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461
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To: pgsql-benchmarks@postgresql.org
Cc: jnasby@pervasive.com, anjankumar@cse.iitb.ac.in, pgsql-hackers@postgresql.org
Subject: Re: Please Help: PostgreSQL Query Optimizer
In-Reply-To: <20051212204003.GY54639@pervasive.com>
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