Re: Oracle db optimizer

On Tuesday, May 20, 2014 3:40:10 AM UTC-6, Jack wrote:
> "joel garry" wrote in message
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> news:609a4cc1-fd8c-4a1d-88aa-113c7d5df5f5_at_googlegroups.com...
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>
>
> On Monday, May 19, 2014 5:59:52 AM UTC-7, Jack wrote:
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> > "Jack" wrote in message news:sshev.40752$SH2.19490_at_uutiset.elisa.fi...
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> >
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> >This isn't really enough information to say, but for whatever reason your
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> >BS table doing a full scan is a much better plan than a bunch of >nested
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> >loops. One could guess the statistics or lack of statistics in the XE is
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> >responsible for that, but better to know than guess. Here is one >simple
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> >methodology for giving us enough information to tell - and you may work it
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> >out just following the steps. Ignore the formatting >advice, of course.
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> >http://oracle-randolf.blogspot.com/2009/02/basic-sql-statement-performance.html
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> >
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> >This all assumes you've gotten the basics from the performance tuning
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> >manual. Jonathan Lewis has a book that explains it in detail, highly
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> > >recommended.
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> >
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> >jg
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> >--
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> >_at_home.com is bogus.
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> >http://www.microscope.co.uk/news/2240220895/Oracle-extends-reach-with-desktop-virtualisation-specialist
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> Thanks jg for your comment.
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>
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> Not sooooo interested to read 27 pages report about plan.
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> Well, no hint available to fix it. (or _dbparameter ?)
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> So I made the logic more simple. Leaving some details away.
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> Some exceptions (and extraordinary exceptionals) are now not counted.
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>
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> But hmm. db 11's costbased optimizer looks very good. No glitches found.
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> Yet.

To fix the problem you need to understand the problem and how Oracle arrived at the problematic plan to begin with. This should be a 'ready, aim, fire' situation, not the usual 'ready, fire, aim' business. That "27 pages report about plan" really *is* worth reading, and the understanding it can give you about your current situation could be invaluable.

We all started at the beginning -- it's the best place to be when you want to understand where you are and what you need to do to go elsewhere.

David Fitzjarrell Received on Tue May 20 2014 - 16:06:46 CEST