e06cc024bd
It's possible to execute user-defined SQL in some background processes; for example, logical replication workers can fire triggers. This opens the possibility that someone would try to execute LISTEN in such a context. But since only regular backends ever call ProcessNotifyInterrupt, no messages would actually be received, and thus the registered listener would simply prevent the message queue from being cleaned. Eventually NOTIFY would stop working, which is bad. Perhaps someday somebody will invent infrastructure to make listening in a background worker actually useful. In the meantime, forbid it. Back-patch to v13, which is where we introduced the MyBackendType variable. It'd be a lot harder to implement the check without that, and it doesn't seem worth the trouble. Discussion: https://postgr.es/m/153243441449.1404.2274116228506175596@wrigleys.postgresql.org
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/.