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From Bryan Pendleton <bpendleton.de...@gmail.com>
Subject Re: Query execution never ends
Date Mon, 22 Mar 2010 15:11:27 GMT
>> Finally, I have both query plans, one for:
>> (Executed successfully in 0.959 s.)
>> http://witoldsz.strefa.pl/queryplan-1.txt
>>
>> and second:
>> (Executed successfully in 2,098.677 s.)
>> http://witoldsz.strefa.pl/queryplan-2.txt

Thank you for sharing the two query plans. They are quite interesting.

Unfortunately, I don't know why Derby is choosing such an inferior plan
for the outer join case, it is quite unfortunate.

I think it would be great if you can file an issue in the Derby tracking
system, and include these discussions, and the query plan information
that you have collected. Perhaps the topic of the issue could be
something like "inferior query plan chosen for outer join".

I agree with you that the query plans are not easy to read. It takes
quite a bit of practice, and I'm still learning, myself.

There does exist a feature in Derby to force certain types of query
plans, using optimizer properties:
http://db.apache.org/derby/docs/10.5/tuning/ctunoptimzoverride.html

It is possible that you could try to force the outer join case to use
the query plan that the inner join case chose, by specifying the
right --DERBY-PROPERTIES information.

I'm afraid that's as much as I know from what I see so far. Hopefully
one of the other Derby users can help you get further with this problem.

thanks,

bryan


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