Thomas Munro 01261fb078 Improve buffer manager API for backend pin limits.
Previously the support functions assumed that the caller needed one pin
to make progress, and could optionally use some more, allowing enough
for every connection to do the same.  Add a couple more functions for
callers that want to know:

* what the maximum possible number could be, irrespective of currently
  held pins, for space planning purposes

* how many additional pins they could acquire right now, without the
  special case allowing one pin, for callers that already hold pins and
  could already make progress even if no extra pins are available

The pin limit logic began in commit 31966b15.  This refactoring is
better suited to read_stream.c, which will be adjusted to respect the
remaining limit as it changes over time in a follow-up commit.  It also
computes MaxProportionalPins up front, to avoid performing divisions
whenever a caller needs to check the balance.

Reviewed-by: Andres Freund <andres@anarazel.de> (earlier versions)
Discussion: https://postgr.es/m/CA%2BhUKGK_%3D4CVmMHvsHjOVrK6t4F%3DLBpFzsrr3R%2BaJYN8kcTfWg%40mail.gmail.com
2025-03-14 17:13:09 +13:00
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2024-11-05 13:56:02 +01:00
2025-01-01 11:21:55 -05:00
2024-02-28 15:17:23 +04:00

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/.

Description
Mirror of the official PostgreSQL GIT repository. Note that this is just a *mirror* - we don't work with pull requests on github. To contribute, please see https://wiki.postgresql.org/wiki/Submitting_a_Patch
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