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Message Posted: Mon, 05 May 2008 @ 23:54:25 GMT


     
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Subj:   Re: Regarding the I/O count
 
From:   McCall, Glenn David

Hi Michael,

The info on index usage is good advice. But how do you know, for example, that Rahul hasn't coded the query poorly and it is doing one or more product joins with a group by or distinct to hide all the extraneous rows? A product join would result in an unnecessarily excessive amount of I/O's and excessive processing times.

IMHO opinion, maybe I'm alone in MHO, but I think that there should be a minimum level of information provided about the problem. This is so that the people who do try to help can do so effectively. There is also a benefit for the asker because there is less chance that (s)he won't get answers that digress from the actual problem.

To be blunt Rahuls question contained no information at all. He simply said (and I'm paraphrasing) "How can I make my query run faster, its doing too many I/O's". By what standard is it doing too many I/O's? For all we know he could be new to TD and is comparing a TD DSS query (millions or billions of I/O's) to an OLTP query (100's of I/O's).

I'm not trying to have a go at anyone (least of all you Michael as I recognise the great contribution you have made to this list).

Maybe it is just me, but there seems to be an increasing number of "my query doesn't work" type posts with little or no information about the details of the problem.

So please question askers, we want to help, but please provide some minimal information. If it is a problem with a query, include the smallest possible query with the problem (not the 10 page monster with a reference to one section of the monster). It's not fair to expect the answerer to trawl through pages of irrelevancy to find the part causing the problem. If it relates to performance, include the explain and index definitions. If it relates to basics (e.g. a syntax question, or a function etc), did you try reading the ("SQL" and "messages reference") manual first? I'm thinking of the "I get a syntax error when I do this" question. Well that's because that syntax isn't allowed and the manual says so!

End of rant


Glenn Mc



     
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