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help / color / mirror / Atom feedFrom: Tender Wang <[email protected]>
To: Richard Guo <[email protected]>
Cc: Paul George <[email protected]>
Cc: Andy Fan <[email protected]>
Cc: PostgreSQL-development <[email protected]>
Cc: [email protected]
Cc: Robert Haas <[email protected]>
Subject: Re: Eager aggregation, take 3
Date: Wed, 11 Sep 2024 10:52:05 +0800
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Richard Guo <[email protected]> 于2024年8月21日周三 15:11写道：
> On Fri, Aug 16, 2024 at 4:14 PM Richard Guo <[email protected]>
> wrote:
> > I had a self-review of this patchset and made some refactoring,
> > especially to the function that creates the RelAggInfo structure for a
> > given relation. While there were no major changes, the code should
> > now be simpler.
>
> I found a bug in v10 patchset: when we generate the GROUP BY clauses
> for the partial aggregation that is pushed down to a non-aggregated
> relation, we may produce a clause with a tleSortGroupRef that
> duplicates one already present in the query's groupClause, which would
> cause problems.
>
> Attached is the updated version of the patchset that fixes this bug
> and includes further code refactoring.
>
>
I continue to review the v11 version patches. Here are some my thoughts.
1. In make_one_rel(), we have the below codes:
/*
* Build grouped base relations for each base rel if possible.
*/
setup_base_grouped_rels(root);
As far as I know, each base rel only has one grouped base relation, if
possible.
The comments may be changed to "Build a grouped base relation for each base
rel if possible."
2. According to the comments of generate_grouped_paths(), we may generate
paths for a grouped
relation on top of paths of join relation. So the ”rel_plain" argument in
generate_grouped_paths() may be
confused. "plain" usually means "base rel" . How about Re-naming rel_plain
to input_rel?
3. In create_partial_grouping_paths(), The partially_grouped_rel could have
been already created due to eager
aggregation. If partially_grouped_rel exists, its reltarget has been
created. So do we need below logic?
/*
* Build target list for partial aggregate paths. These paths cannot just
* emit the same tlist as regular aggregate paths, because (1) we must
* include Vars and Aggrefs needed in HAVING, which might not appear in
* the result tlist, and (2) the Aggrefs must be set in partial mode.
*/
partially_grouped_rel->reltarget =
make_partial_grouping_target(root, grouped_rel->reltarget,
extra->havingQual);
--
Thanks,
Tender Wang
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Subject: Re: Eager aggregation, take 3
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