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 > ------- > u2-users mailing list > u2-users@listserver.u2ug.org > To unsubscribe please visit http://listserver.u2ug.org/ >
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 ------- u2-users mailing list u2-users@listserver.u2ug.org To unsubscribe please visit http://listserver.u2ug.org/