On Tue, 7 Jun 2005 [EMAIL PROTECTED] wrote:
> I think we have to keep in mind what happens in the whole process.
> While the select itself will process faster (provided you have not specified
> NO.NULLS when creating the index), we have to ask what you're going to do next
> with that list ?
>
> If the amount of nulls exceeds perhaps, off-the-cuff, ten percent of your
> database, then you will not enjoy any end-to-end speed improvements in your
> process. This is because, in processing that list, you will be jumping all
> over
> your disk in semi-random order. (Let's assume the entire file is not resident
> in memory at once.) Because of this "thrashing", each READ will take
> significantly longer than if you simply read the file, in hashed order, from
> beginning
> to end, and process only those records with nulls in your target field.
>
> So in the end, your timing may show, that an indexed SELECT on a value that
> is very common, followed by a loop of processing, is actually taking longer,
> than a non-indexed SELECT, followed by that same loop.
>
> And you thought this stuff was easy :)
>
> Will Johnson
> Fast Forward Technologies
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Jeff Butera, Ph.D.
Administrative Systems
Hampshire College
[EMAIL PROTECTED]
413-559-5556
"...our behavior matters more than the beliefs that we profess."
Elizabeth Deutsch Earle
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