Horton

Re: Eager aggregation, take 3

Matheus Alcantara <matheusssilv97@gmail.com>

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From: "Matheus Alcantara" <matheusssilv97@gmail.com>
To: "Richard Guo" <guofenglinux@gmail.com>, "David Rowley" <dgrowleyml@gmail.com>
Cc: "Robert Haas" <robertmhaas@gmail.com>, "Tom Lane" <tgl@sss.pgh.pa.us>, "Tender Wang" <tndrwang@gmail.com>, "Paul George" <p.a.george19@gmail.com>, "Andy Fan" <zhihuifan1213@163.com>, "PostgreSQL-development" <pgsql-hackers@postgresql.org>, <pgsql-hackers@lists.postgresql.org>
Date: 2026-04-02T12:18:50Z
Lists: pgsql-hackers

Attachments

On Mon Mar 30, 2026 at 12:17 AM -03, Richard Guo wrote:
> On Thu, Oct 9, 2025 at 5:07 PM Richard Guo <guofenglinux@gmail.com> wrote:
>> I noticed an unnecessary header include in initsplan.c.  Will fix that
>> as well.
>
> I noticed a couple of issues that can lead to unexpected results.
> I've attached two patches to fix them.
>
> 1. Eager aggregation was incorrectly checking the data type's default
> collation rather than the expression's actual collation.  This allowed
> columns with non-deterministic collations to be pushed down, resulting
> in incorrect grouping.  Fixed by 0001.
>
> 2. Pushing aggregates containing volatile functions below a join
> alters their execution count.  Fixed by 0002.
>
> (As briefly discussed on Discord, this non-deterministic collation
> issue also exists in our long-existing logic for pushing HAVING down
> to WHERE.  But let's fix it for the eager aggregation first.)
>

Hi Richard,

The patches looks good to me and are working as expected. It seems very
straightforward, so I don't have any major comments.

I'm attaching some new tests that I've added to collate.icu.utf8 and
eager_aggregate regression tests during my review, fell free to include
any of them if it could be helpful or none.

--
Matheus Alcantara
EDB: https://www.enterprisedb.com

Commits

  1. Fix eager aggregation for semi/antijoin inner rels

  2. Cover additional errors and corner conditions in repack.c

  3. Fix volatile function evaluation in eager aggregation

  4. Fix collation handling for grouping keys in eager aggregation

  5. Rename apply_at to apply_agg_at for clarity

  6. Fix comment in eager_aggregate.sql

  7. Remove unnecessary include of "utils/fmgroids.h"

  8. Implement Eager Aggregation

  9. Allow negative aggtransspace to indicate unbounded state size

  10. Add macros for looping through a List without a ListCell.

  11. Account for the effect of lossy pages when costing bitmap scans.

  12. Fix a thinko in join_is_legal: when we decide we can implement a semijoin