From: | Andres Freund <andres(at)anarazel(dot)de> |
---|---|
To: | pgsql-hackers(at)postgresql(dot)org |
Cc: | Jan Urbański <wulczer(at)wulczer(dot)org> |
Subject: | Re: join ordering via Simulated Annealing |
Date: | 2009-12-26 16:30:54 |
Message-ID: | 200912261730.54730.andres@anarazel.de |
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Lists: | pgsql-hackers |
On Wednesday 23 December 2009 02:23:55 Jan Urbański wrote:
> Hi,
>
> I've been playing with using a Simulated Annealing-type algorithm for
> determinig join ordering for relations.
Very cool.
> 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
http://archives.postgresql.org/message-
id/200907091700(dot)43411(dot)andres(at)anarazel(dot)de
which tom analyzed and improved here http://archives.postgresql.org/message-
id/17807(dot)1247932094(at)sss(dot)pgh(dot)pa(dot)us
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
interesting.
Andres
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