> -----Original Message-----
> From: Alex Turner [mailto:[EMAIL PROTECTED]
> Sent: Monday, April 18, 2005 5:50 PM
> To: Bruce Momjian
> Cc: Kevin Brown; pgsql-performance@postgresql.org
> Subject: Re: [PERFORM] How to improve db performance with $7K?
> Does it really matter at which end of the cable the queueing is done
> (Assuming both ends know as much about drive geometry etc..)?
> [...]

The parenthetical is an assumption I'd rather not make.  If my
performance depends on my kernel knowing how my drive is laid
out, I would always be wondering if a new drive is going to 
break any of the kernel's geometry assumptions.  Drive geometry
doesn't seem like a kernel's business any more than a kernel
should be able to decode the ccd signal of an optical mouse.
The kernel should queue requests at a level of abstraction that
doesn't depend on intimate knowledge of drive geometry, and the
drive should queue requests on the concrete level where geometry
matters.  A drive shouldn't guess whether a process is trying to
read a file sequentially, and a kernel shouldn't guess whether
sector 30 is contiguous with sector 31 or not.

David B. Held
Software Engineer/Array Services Group
200 14th Ave. East,  Sartell, MN 56377
320.534.3637 320.253.7800 800.752.8129

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