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From Witold Szczerba <pljosh.m...@gmail.com>
Subject Re: Query execution never ends
Date Mon, 22 Mar 2010 15:43:07 GMT
2010/3/22 Bryan Pendleton <bpendleton.derby@gmail.com>:
>>> 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

I will try to compare those query plans with the ones used by derby on
empty database. If they would match, I could attach an empty database
in Derby bug tracking system - that could help diagnose the issue,
maybe Derby will gain from this case.

By the way: I am sure that little things like unreadable query plans
and/or lack of some basic tools to display them are one of causes
there are so few people using Derby database. Before I picked this
database for a project, I was asking friends and on usenet if someone
actually use it - no one did. Commercial products also bypass Derby -
yesterday I was evaluating AquaFold's Data Studio - they said they
support Derby and I saw nice visual query plans (tree and diagrams).
My first (and last) attempt ended in a dialog box: visual explain
plans not supported for Derby :(

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