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Since its introduction, max_wal_senders is counted as part of max_connections when it comes to define how many connection slots can be used for replication connections with a WAL sender context. This can lead to confusion for some users, as it could be possible to block a base backup or replication from happening because other backend sessions are already taken for other purposes by an application, and superuser-only connection slots are not a correct solution to handle that case. This commit makes max_wal_senders independent of max_connections for its handling of PGPROC entries in ProcGlobal, meaning that connection slots for WAL senders are handled using their own free queue, like autovacuum workers and bgworkers. One compatibility issue that this change creates is that a standby now requires to have a value of max_wal_senders at least equal to its primary. So, if a standby created enforces the value of max_wal_senders to be lower than that, then this could break failovers. Normally this should not be an issue though, as any settings of a standby are inherited from its primary as postgresql.conf gets normally copied as part of a base backup, so parameters would be consistent. Author: Alexander Kukushkin Reviewed-by: Kyotaro Horiguchi, Petr Jelínek, Masahiko Sawada, Oleksii Kliukin Discussion: https://postgr.es/m/CAFh8B=nBzHQeYAu0b8fjK-AF1X4+_p6GRtwG+cCgs6Vci2uRuQ@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/.