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Nathan Bossart 8b2bcf3f28 Introduce the dynamic shared memory registry.
Presently, the most straightforward way for a shared library to use
shared memory is to request it at server startup via a
shmem_request_hook, which requires specifying the library in
shared_preload_libraries.  Alternatively, the library can create a
dynamic shared memory (DSM) segment, but absent a shared location
to store the segment's handle, other backends cannot use it.  This
commit introduces a registry for DSM segments so that these other
backends can look up existing segments with a library-specified
string.  This allows libraries to easily use shared memory without
needing to request it at server startup.

The registry is accessed via the new GetNamedDSMSegment() function.
This function handles allocating the segment and initializing it
via a provided callback.  If another backend already created and
initialized the segment, it simply attaches the segment.
GetNamedDSMSegment() locks the registry appropriately to ensure
that only one backend initializes the segment and that all other
backends just attach it.

The registry itself is comprised of a dshash table that stores the
DSM segment handles keyed by a library-specified string.

Reviewed-by: Michael Paquier, Andrei Lepikhov, Nikita Malakhov, Robert Haas, Bharath Rupireddy, Zhang Mingli, Amul Sul
Discussion: https://postgr.es/m/20231205034647.GA2705267%40nathanxps13
2024-01-19 14:24:36 -06:00
config Add copyright notices to a few perl scripts that don't have them 2024-01-05 13:15:50 +00:00
contrib Add stratnum GiST support function 2024-01-19 15:42:13 +01:00
doc Introduce the dynamic shared memory registry. 2024-01-19 14:24:36 -06:00
src Introduce the dynamic shared memory registry. 2024-01-19 14:24:36 -06:00
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.cirrus.tasks.yml Use "template" data directory in tests 2023-08-24 14:38:02 -07:00
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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/.