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Re: review: More frame options in window functions

From: Hitoshi Harada <umi(dot)tanuki(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: review: More frame options in window functions
Date: 2010-02-13 06:42:05
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Lists: pgsql-hackers
2010/2/13 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:
> Hitoshi Harada <umi(dot)tanuki(at)gmail(dot)com> writes:
>> [ more_frame_options patch ]
> Committed after rather extensive revisions.

Thanks a lot.

> I'm not terribly happy with the changes you made in WinGetFuncArgInPartition
> and WinGetFuncArgInFrame to force the window function mark to not go
> past frame start in some modes.  Not only is that pretty ugly, but I
> think it can mask bugs in window functions: it's an error for a window
> function to fetch a row before what it has set its mark to be, but in
> some cases that wouldn't be detected because of this change.  I think
> it would be better to revert those changes and find another method of
> protecting fetches needed to determine the frame head.  One idea is
> to create a separate read pointer that tracks the frame head whenever
> actual fetches of the frame head might be needed by update_frameheadpos.
> I committed it without changing that, but I think this should be
> revisited before trying to add the RANGE value PRECEDING/FOLLOWING
> options, because those will substantially expand the number of cases
> where that hack affects the behavior.

Well, you're right. In addition to this topic, I concern a little
about changing row fetching in aggregate from spool_tuples() to
window_gettupleslot(), for performance reason. It's needed to support
extended frame options, but for original basic frame options it may
get slow. Anyway, I agree to revisit and refactor to executor logic.


Hitoshi Harada

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