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help / color / mirror / Atom feedFrom: Robert Haas <rhaas@postgresql.org>
To: pgsql-committers@lists.postgresql.org
Subject: pgsql: Change GEQO fitness comparisons to consider disabled_nodes.
Date: Thu, 17 Sep 2026 13:47:33 +0000
Message-ID: <E1x7CSb-000000007Sm-2jVK@gemulon.postgresql.org> (raw)
Change GEQO fitness comparisons to consider disabled_nodes.
Prior to v18, the total cost of a plan was just one number, a
floating-point value. Commit e22253467942fdb100087787c3e1e3a8620c54b2
introduced a second component, the number of disabled_nodes at or
below that level of the plan tree. Unfortunately, I (rhaas) failed
to realize that GEQO extracts the cost from each candidate plan and
compares it directly as a measure of fitness.
This means that, at least in principle, it's possible for GEQO to
prefer a plan with more disabled_nodes and lower cost over one with
fewer disabled_nodes and higher cost, which is incorrect. It may be
possible for that to become a practical issue in v18, but it's much
more likely to become an issue in v19 due to pg_plan_advice. Hence,
since the straightforward fix breaks ABI compatibility, back-patch
only to v19.
Backpatch-through: 19
Discussion: https://postgr.es/m/CA+TgmoYmXy-jiP5qDhqNEiYFEBzQsArO6O2d9E8szNZqi1bePQ@mail.gmail.com
Branch
------
REL_19_STABLE
Details
-------
https://git.postgresql.org/pg/commitdiff/d22961bca2c8076c05546bf2fb83fdf5df81e843
Modified Files
--------------
src/backend/optimizer/geqo/geqo_eval.c | 18 ++++++++++------
src/backend/optimizer/geqo/geqo_main.c | 13 +++++++-----
src/backend/optimizer/geqo/geqo_misc.c | 19 +++++++++++------
src/backend/optimizer/geqo/geqo_pool.c | 29 ++++++++++---------------
src/include/optimizer/geqo.h | 2 +-
src/include/optimizer/geqo_gene.h | 39 +++++++++++++++++++++++++++++++++-
src/tools/pgindent/typedefs.list | 1 +
7 files changed, 82 insertions(+), 39 deletions(-)
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To: pgsql-committers@postgresql.org
Cc: rhaas@postgresql.org, pgsql-committers@lists.postgresql.org
Subject: Re: pgsql: Change GEQO fitness comparisons to consider disabled_nodes.
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