postgresql

mirror of https://git.postgresql.org/git/postgresql.git synced 2024-09-28 22:51:53 +02:00

Go to file

David Rowley 3226f47282 Add enable_presorted_aggregate GUC `1349d279` added query planner support to allow more efficient execution of aggregate functions which have an ORDER BY or a DISTINCT clause. Prior to that commit, the planner would only request that the lower planner produce a plan with the order required for the GROUP BY clause and it would be left up to nodeAgg.c to perform the final sort of records within each group so that the aggregate transition functions were called in the correct order. Now that the planner requests the lower planner produce a plan with the GROUP BY and the ORDER BY / DISTINCT aggregates in mind, there is the possibility that the planner chooses a plan which could be less efficient than what would have been produced before `1349d279`. While developing `1349d279`, I had in mind that Incremental Sort would help us in cases where an index exists only on the GROUP BY column(s). Incremental Sort would just replace the implicit tuplesorts which are being performed in nodeAgg.c. However, because the planner has the flexibility to instead choose a plan which just performs a full sort on both the GROUP BY and ORDER BY / DISTINCT aggregate columns, there is potential for the planner to make a bad choice. The costing for Incremental Sort is not perfect as it assumes an even distribution of rows to sort within each sort group. Here we add an escape hatch in the form of the enable_presorted_aggregate GUC. This will allow users to get the pre-PG16 behavior in cases where they have no other means to convince the query planner to produce a plan which only sorts on the GROUP BY column(s). Discussion: https://postgr.es/m/CAApHDvr1Sm+g9hbv4REOVuvQKeDWXcKUAhmbK5K+dfun0s9CvA@mail.gmail.com		2022-12-20 22:28:58 +13:00
config	autoconf: Move export_dynamic determination to configure	2022-12-06 18:55:28 -08:00
contrib	C comment: fix wording	2022-12-16 12:15:54 -05:00
doc	Add enable_presorted_aggregate GUC	2022-12-20 22:28:58 +13:00
src	Add enable_presorted_aggregate GUC	2022-12-20 22:28:58 +13:00
.cirrus.yml	Add option to specify segment size in blocks	2022-12-07 19:32:59 -08:00
.dir-locals.el
.editorconfig
.git-blame-ignore-revs
.gitattributes
.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	Disable clang 16's -Wcast-function-type-strict.	2022-12-13 10:15:56 +13:00
configure.ac	Disable clang 16's -Wcast-function-type-strict.	2022-12-13 10:15:56 +13:00
COPYRIGHT
GNUmakefile.in	Remove temporary portlock directory during make [dist]clean.	2022-11-26 10:30:31 -05:00
HISTORY
Makefile
meson_options.txt	Add option to specify segment size in blocks	2022-12-07 19:32:59 -08:00
meson.build	Disable clang 16's -Wcast-function-type-strict.	2022-12-13 10:15:56 +13:00
README
README.git

README

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.

PostgreSQL has many language interfaces, many of which are listed here:

	https://www.postgresql.org/download/

See the file INSTALL for instructions on how to build and install
PostgreSQL.  That file also lists supported operating systems and
hardware platforms and contains information regarding any other
software packages that are required to build or run the PostgreSQL
system.  Copyright and license information can be found in the
file COPYRIGHT.  A comprehensive documentation set is included in this
distribution; it can be read as described in the installation
instructions.

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