Re: Please Help: PostgreSQL Query Optimizer

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
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