In PostgreSQL, every database connection is a separate process. All those processes are synchronized using shared memory (technically, in most cases it is mapped memory, but for this example, that makes no difference). This shared memory contains the I/O cache, the list of active database connections, locks, and more vital stuff which makes the system function properly.
When a connection is closed, it will remove all relevant entries from shared memory and leave the system in a sane state. However, what happens when a database connection simply crashes for whatever reason?
The postmaster (the main process) will detect that one of the child processes is missing. Then, all other connections will be terminated ...
