Re: Window function optimisation, allow pushdowns of items matching PARTITION BY clauses

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От David Rowley
Тема Re: Window function optimisation, allow pushdowns of items matching PARTITION BY clauses
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Msg-id CAHoyFK9ihoSarntWc-NJ5tPHko4Wcausd-1C_0wEcogi9UEKTw@mail.gmail.com
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Ответ на Re: Window function optimisation, allow pushdowns of items matching PARTITION BY clauses  (Tom Lane <tgl@sss.pgh.pa.us>)
Ответы Re: Window function optimisation, allow pushdowns of items matching PARTITION BY clauses  (Thomas Mayer <thomas.mayer@student.kit.edu>)
Re: Window function optimisation, allow pushdowns of items matching PARTITION BY clauses  (Vik Fearing <vik.fearing@dalibo.com>)
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On 14 April 2014 03:31, Tom Lane <tgl@sss.pgh.pa.us> wrote:
David Rowley <dgrowley@gmail.com> writes:
> On this thread
> http://www.postgresql.org/message-id/52C6F712.6040804@student.kit.edu there
> was some discussion around allowing push downs of quals that happen to be
> in every window clause of the sub query. I've quickly put together a patch
> which does this (see attached)

I think you should have check_output_expressions deal with this, instead.
Compare the existing test there for non-DISTINCT output columns.


I've moved the code there and it seems like a much better place for it. Thanks for the tip.
 
> Oh and I know that my function var_exists_in_all_query_partition_by_clauses
> has no business in allpaths.c, I'll move it out as soon as I find a better
> home for it.

I might be wrong, but I think you could just embed that search loop in
check_output_expressions, and it wouldn't be too ugly.


I've changed the helper function to take the TargetEntry now the same as targetIsInSortList does for the hasDistinctOn test and I renamed the helper function to targetExistsInAllQueryPartitionByClauses. It seems much better, but there's probably a bit of room for improving on the names some more.

I've included the updated patch with some regression tests.
The final test I added tests that an unused window which would, if used, cause the pushdown not to take place still stops the pushdownf from happening... I know you both talked about this case in the other thread, but I've done nothing for it as Tom mentioned that this should likely be fixed elsewhere, if it's even worth worrying about at all. I'm not quite sure if I needed to bother including this test for it, but I did anyway, it can be removed if it is deemed unneeded.

Per Thomas' comments, I added a couple of tests that ensure that the order of the columns in the partition by clause don't change the behaviour. Looking at the implementation of the actual code makes this test seems a bit unneeded as really but I thought that the test should not assume anything about the implementation so from that point of view the extra test seems like a good idea.

For now I can't think of much else to do for the patch, but I'd really appreciate it Thomas if you could run it through the paces if you can find any time for it, or maybe just give my regression tests a once over to see if you can think of any other cases that should be covered.

Regards

David Rowley
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