mirror of
https://github.com/postgres/postgres.git
synced 2025-06-13 07:41:39 +03:00
efdcca55a3
In nodeAppend.c and nodeMergeAppend.c there were some foreach loops which
looped over the list of subplans and only performed any work if the
subplan index was found in a Bitmapset. With the old linked list
implementation of List, this form made sense as accessing the Nth list
element was O(N). However, thanks to 1cff1b95a we now have array-based
lists, so accessing the Nth element has become O(1).
Here we make the most of the O(1) lookups and just loop over the set
members of the Bitmapset with bms_next_member(). This performs slightly
better when a small number of the list items are in the Bitmapset. Micro
benchmarks show that when the Bitmapset contains all or most of the list
items then the new code is ever so slightly slower. In practice, the cost
is so small that it's drowned out by various other things such as locking
the relations belonging to each subplan, etc.
The primary goal here is to leave better code examples around which benefit
better from the new list implementation.
Reviewed-by: Tom Lane
Discussion: https://postgr.es/m/CAKJS1f8ZcsLVgkF4wOfRyMYTcPgLFiUAOedFC+U2vK_aFZk-BA@mail.gmail.com
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/.