| From: | "Jim C(dot) Nasby" <jnasby(at)pervasive(dot)com> |
|---|---|
| To: | "Anjan Kumar(dot) A(dot)" <anjankumar(at)cse(dot)iitb(dot)ac(dot)in> |
| Cc: | pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Please Help: PostgreSQL Query Optimizer |
| Date: | 2005-12-12 20:40:03 |
| Message-ID: | 20051212204003.GY54639@pervasive.com |
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| Lists: | pgsql-benchmarks pgsql-chat pgsql-docs pgsql-hackers |
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(at)pervasive(dot)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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