Horton

Re: Eager aggregation, take 3

Richard Guo <guofenglinux@gmail.com>

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From: Richard Guo <guofenglinux@gmail.com>
To: 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, Matheus Alcantara <matheusssilv97@gmail.com>
Date: 2026-03-30T03:17:03Z
Lists: pgsql-hackers

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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.)

- Richard

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