Background Workers are processes that run under the monitoring of the cluster itself, which means they have a life cycle bound to the life cycle of the cluster itself. Background Workers are a special kind of process: they can plug in as extensions and can exploit PostgreSQL's internal features, most notably its shared memory (where the data resides at runtime).
We can use background workers to form the communication infrastructure in the publish-subscribe model of the logical replication introduced with PostgreSQL 10, even though background workers are actually older than that.
Background Workers are written in the C language, compiled against the PostgreSQL version, and loaded at runtime as shared libraries. Since these processes can access PostgreSQL's internal data structures, they represent both a powerful and possibly dangerous way to extend...