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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
2024-10-16 12:17:49 -04:00
.github Add CODE_OF_CONDUCT.md, CONTRIBUTING.md, and SECURITY.md. 2024-07-02 13:03:58 -05:00
config Simplify checking for xlocale.h 2024-10-01 07:23:45 -04:00
contrib Add contrib/pg_logicalinspect. 2024-10-14 17:22:02 -07:00
doc initdb: Change default to using data checksums. 2024-10-16 08:48:10 +02:00
src Normalize nbtree truncated high key array behavior. 2024-10-16 12:17:49 -04:00
.cirrus.star Remove duplicate words in docs and code comments. 2023-10-09 09:18:47 +05:30
.cirrus.tasks.yml Add PG_TEST_PG_COMBINEBACKUP_MODE to CI tasks 2024-09-10 16:30:38 +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 commit 7f7474a8e4 to .git-blame-ignore-revs. 2024-10-14 15:09:39 -05:00
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.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 Remove traces of BeOS. 2024-10-14 08:33:36 +02:00
configure.ac Remove traces of BeOS. 2024-10-14 08:33:36 +02:00
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 Simplify checking for xlocale.h 2024-10-01 07:23:45 -04:00
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/.