c9c660e6ae
Prior to v18, the total cost of a plan was just one number, a
floating-point value. Commit e222534679
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
PostgreSQL Database Management System
This directory contains the source code distribution of the PostgreSQL database management system.
PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings.
Copyright and license information can be found in the file COPYRIGHT.
General documentation about this version of PostgreSQL can be found at https://www.postgresql.org/docs/devel/. In particular, information about building PostgreSQL from the source code can be found at https://www.postgresql.org/docs/devel/installation.html.
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