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Thomas Munro 4effd0844d Fix unfairness in all-cached parallel seq scan. 
Commit b5a9b18c introduced block streaming infrastructure with a special
fast path for all-cached scans, and commit b7b0f3f2 connected the
infrastructure up to sequential scans.  One of the fast path
micro-optimizations had an unintended consequence: it interfered with
parallel sequential scan's block range allocator (from commit 56788d21),
which has its own ramp-up and ramp-down algorithm when handing out
groups of pages to workers.  A scan of an all-cached table could give
extra blocks to one worker, when others had finished.  In some plans
(probably already very bad plans, such as the one reported by
Alexander), the unfairness could be magnified.

An internal buffer of 16 block numbers is removed, keeping just a single
block buffer for technical reasons.

Back-patch to 17.

Reported-by: Alexander Lakhin <exclusion@gmail.com>
Discussion: https://postgr.es/m/63a63690-dd92-c809-0b47-af05459e95d1%40gmail.com
2024-08-31 17:28:02 +12:00
.github Add CODE_OF_CONDUCT.md, CONTRIBUTING.md, and SECURITY.md. 2024-07-02 13:03:58 -05:00
config jit: Remove {llvm-config,clang}-N configure probes. 2024-05-16 13:58:25 +12:00
contrib Make postgres_fdw's query_cancel test less flaky. 2024-08-30 16:47:39 -04:00
doc Clarify restrict_nonsystem_relation_kind description. 2024-08-30 15:06:09 -07:00
src Fix unfairness in all-cached parallel seq scan. 2024-08-31 17:28:02 +12:00
.cirrus.star Remove duplicate words in docs and code comments. 2023-10-09 09:18:47 +05:30
.cirrus.tasks.yml Convert node test compile-time settings into run-time parameters 2024-08-01 10:09:18 +02:00
.cirrus.yml ci: Make compute resources for CI configurable 2023-08-23 15:15:28 -07:00
.dir-locals.el Make Emacs perl-mode indent more like perltidy. 2019-01-13 11:32:31 -08:00
.editorconfig Add .editorconfig 2019-12-18 09:13:13 +01:00
.git-blame-ignore-revs Add 97add39c0 to .git-blame-ignore-revs. 2024-08-15 11:43:55 -04:00
.gitattributes Remove non-existing file from .gitattributes 2024-02-16 11:39:09 +01:00
.gitignore Update top-level .gitignore. 2022-12-04 15:23:00 -05:00
aclocal.m4 autoconf: Move export_dynamic determination to configure 2022-12-06 18:55:28 -08:00
configure Improve configure error for ICU libraries if pkg-config is absent. 2024-08-20 12:25:06 -07:00
configure.ac Improve configure error for ICU libraries if pkg-config is absent. 2024-08-20 12:25:06 -07:00
COPYRIGHT Update copyright for 2024 2024-01-03 20:49:05 -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 Remove AIX support 2024-02-28 15:17:23 +04:00
meson.build thread-safety: gmtime_r(), localtime_r() 2024-08-23 07:43:04 +02:00
meson_options.txt Remove spinlocks and atomics from meson_options.txt. 2024-07-30 23:37:14 +12:00
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/.