Peter Geoghegan 79fa7b3b1a Normalize nbtree truncated high key array behavior. Commit `5bf748b8` taught nbtree ScalarArrayOp index scans to decide when and how to start the next primitive index scan based on physical index characteristics. This included rules for deciding whether to start a new primitive index scan (or whether to move onto the right sibling leaf page instead) that specifically consider truncated lower-order columns (-inf columns) from leaf page high keys. These omitted columns were treated as satisfying the scan's required scan keys, though only for scan keys marked required in the current scan direction (forward). Scan keys that didn't get this behavior (those marked required in the backwards direction only) usually didn't give the scan reasonable cause to reposition itself to a later leaf page (via another descent of the index in _bt_first), but _bt_advance_array_keys would nevertheless always give up by forcing another call to _bt_first. _bt_advance_array_keys was unwilling to allow the scan to continue onto the next leaf page, to reconsider whether we really should start another primitive scan based on the details of the sibling page's tuples. This didn't match its behavior with similar cases involving keys required in the current scan direction (forward), which seems unprincipled. It led to an excessive number of primitive scans/index descents for queries with a higher-order = array scan key (with dense, contiguous values) mixed with a lower-order required > or >= scan key. Bring > and >= strategy scan keys in line with other required scan key types: treat truncated -inf scan keys as having satisfied scan keys required in either scan direction (forwards and backwards alike) during array advancement. That way affected scans can continue to the right sibling leaf page. Advancement must now schedule an explicit recheck of the right sibling page's high key in cases involving > or >= scan keys. The recheck gives the scan a way to back out and start another primitive index scan (we can't just rely on _bt_checkkeys with > or >= scan keys). This work can be considered a stand alone optimization on top of the work from commit `5bf748b8`. But it was written in preparation for an upcoming patch that will add skip scan to nbtree. In practice scans that use "skip arrays" will tend to be much more sensitive to any implementation deficiencies in this area. Author: Peter Geoghegan <pg@bowt.ie> Reviewed-By: Tomas Vondra <tomas@vondra.me> Discussion: https://postgr.es/m/CAH2-Wz=9A_UtM7HzUThSkQ+BcrQsQZuNhWOvQWK06PRkEp=SKQ@mail.gmail.com		2 years ago
.github	Add CODE_OF_CONDUCT.md, CONTRIBUTING.md, and SECURITY.md.	2 years ago
config	Simplify checking for xlocale.h	2 years ago
contrib	Add contrib/pg_logicalinspect.	2 years ago
doc	initdb: Change default to using data checksums.	2 years ago
src	Normalize nbtree truncated high key array behavior.	2 years ago
.cirrus.star	Remove duplicate words in docs and code comments.	3 years ago
.cirrus.tasks.yml	Add PG_TEST_PG_COMBINEBACKUP_MODE to CI tasks	2 years ago
.cirrus.yml	ci: Make compute resources for CI configurable	3 years ago
.dir-locals.el	Make Emacs perl-mode indent more like perltidy.	7 years ago
.editorconfig	Add .editorconfig	6 years ago
.git-blame-ignore-revs	Add commit `7f7474a8e4` to .git-blame-ignore-revs.	2 years ago
.gitattributes	Remove non-existing file from .gitattributes	2 years ago
.gitignore	Update top-level .gitignore.	3 years ago
COPYRIGHT	Update copyright for 2024	2 years ago
GNUmakefile.in	Allow selecting the git revision to be packaged by "make dist".	2 years ago
HISTORY	Canonicalize some URLs	6 years ago
Makefile	Remove AIX support	2 years ago
README.md	Revise the style of a paragraph in README.md.	2 years ago
aclocal.m4	autoconf: Move export_dynamic determination to configure	3 years ago
configure	Remove traces of BeOS.	2 years ago
configure.ac	Remove traces of BeOS.	2 years ago
meson.build	Simplify checking for xlocale.h	2 years ago
meson_options.txt	Remove spinlocks and atomics from meson_options.txt.	2 years ago

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.

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/.