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From Oyvind.Bakk...@Sun.COM
Subject Re: derby performance and 'order by'
Date Thu, 22 Sep 2005 07:14:32 GMT
Rick Hillegas wrote:
> Hi Oyvind,
> 
> I agree that this is inelegant. As you note, this approach step by step 
> forces a plan which the current Derby optimizer is capable of 
> considering--with or without the covering index. Regardless of whether 
> we teach the optimizer some better tricks, I think it's worth beefing up 
> our support for in-memory temporary tables:
> 
> o There are always deceptively simple queries which the optimizer 
> misjudges. It's good to give the customer tools for getting unstuck 
> while they wait for the bugfix release.
> 
> o Often the customer knows facts about the data which the optimizer 
> can't plausibly learn.

Yes, I agree with you.

> o The current Derby optimizer is capable of considering only a very 
> limited subset of the useful plans.

That reminds me of a very entertaining presentation which was held at 
VLDB this year:

Slides: http://www.vldb2005.org/program/slides/fri/s1228-reddy.ppt
Paper: http://www.vldb2005.org/program/paper/fri/p1228-reddy.pdf

Have a look, it's worth the time.

We should definitely consider more execution plans in Derby, so that we, 
too, could draw such interesting pictures. ;o)

-- 
Oyvind Bakksjo
Sun Microsystems, Database Technology Group
Trondheim, Norway
http://weblogs.java.net/blog/bakksjo/

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