|From:||Andres Freund <andres(at)anarazel(dot)de>|
|Cc:||Jan Urbański <wulczer(at)wulczer(dot)org>|
|Subject:||Re: join ordering via Simulated Annealing|
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On Wednesday 23 December 2009 02:23:55 Jan Urbański wrote:
> I've been playing with using a Simulated Annealing-type algorithm for
> determinig join ordering for relations.
> Lastly, I'm lacking good testcases or even a testing approach: I'm
> generating silly queries and looking at how they get optimised, but if
> someone has a real dataset and examples of joins that cannot be planned
> with the standard planner, I would be interested to compare the results
> my prototype gets with those produced by GEQO.
If you want to see some queries which are rather hard to plan with random
search you can look at
which tom analyzed and improved here http://archives.postgresql.org/message-
They are hard to plan because they have lots and lots of join order
restrictions. While this example is rather extreme I have found quite many
such queries so far.
Robert had another example in
603c8f070911271205r4d4534edt1cebcb76ff5066a5(at)mail(dot)gmail(dot)com that might be
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