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Robert Haas 8300d3ad4a Consider startup cost as a figure of merit for partial paths. 
Previously, the comments stated that there was no purpose to considering
startup cost for partial paths, but this is not the case: it's perfectly
reasonable to want a fast-start path for a plan that involves a LIMIT
(perhaps over an aggregate, so that there is enough data being processed
to justify parallel query but yet we don't want all the result rows).

Accordingly, rewrite add_partial_path and add_partial_path_precheck to
consider startup costs. This also fixes an independent bug in
add_partial_path_precheck: commit e222534679
failed to update it to do anything with the new disabled_nodes field.
That bug fix is formally separate from the rest of this patch and could
be committed separately, but I think it makes more sense to fix both
issues together, because then we can (as this commit does) just make
add_partial_path_precheck do the cost comparisons in the same way as
compare_path_costs_fuzzily, which hopefully reduces the chances of
ending up with something that's still incorrect.

This patch is based on earlier work on this topic by Tomas Vondra,
but I have rewritten a great deal of it.

Co-authored-by: Robert Haas <rhaas@postgresql.org>
Co-authored-by: Tomas Vondra <tomas@vondra.me>
Discussion: http://postgr.es/m/CA+TgmobRufbUSksBoxytGJS1P+mQY4rWctCk-d0iAUO6-k9Wrg@mail.gmail.com
2026-03-09 08:16:30 -04:00
.github Add CODE_OF_CONDUCT.md, CONTRIBUTING.md, and SECURITY.md. 2024-07-02 13:03:58 -05:00
config Portable StaticAssertExpr 2026-03-06 09:27:54 +01:00
contrib CREATE SUBSCRIPTION ... SERVER. 2026-03-06 08:27:56 -08:00
doc doc: Document IF NOT EXISTS option for ALTER FOREIGN TABLE ADD COLUMN. 2026-03-09 18:23:36 +09:00
src Consider startup cost as a figure of merit for partial paths. 2026-03-09 08:16:30 -04:00
.cirrus.star ci: Simplify ci-os-only handling 2025-08-14 12:09:34 -04:00
.cirrus.tasks.yml Revert "Change default value of default_toast_compression to "lz4"" 2026-03-05 08:25:35 +09:00
.cirrus.yml ci: Per-repo configuration for manually trigger tasks 2025-08-14 11:54:03 -04:00
.dir-locals.el Make Emacs perl-mode indent more like perltidy. 2019-01-13 11:32:31 -08:00
.editorconfig Update .editorconfig and .gitattributes for postgresql.conf.sample. 2025-11-18 10:28:36 -06:00
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aclocal.m4 autoconf: Move export_dynamic determination to configure 2022-12-06 18:55:28 -08:00
configure Move comment back to better place 2026-03-09 10:36:16 +01:00
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COPYRIGHT Update copyright for 2026 2026-01-01 13:24:10 -05:00
GNUmakefile.in Allow selecting the git revision to be packaged by "make dist". 2024-05-03 11:08:50 -04:00
HISTORY Canonicalize some URLs 2020-02-10 20:47:50 +01:00
Makefile Restore AIX support. 2026-02-23 13:34:22 -05:00
meson.build Portable StaticAssertExpr 2026-03-06 09:27:54 +01:00
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README.md Revise the style of a paragraph in README.md. 2024-03-21 10:16:41 -05:00

README.md

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.

The latest version of this software, and related software, may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.