Why are there multiple instances of postgres running in the background after restart?

Question

Why are there multiple instances of postgres running in the background after restart?

How can I configure it not to start on booting up the system?

Answer 1

That's perfectly normal.

Postgres uses a multi-process architecture rather than a multi-threaded architecture.

Those are not "multiple instances", but the background processes that Postgres creates during the server startup (because of its multi-process architecture).

See Who has any documents that about PostgreSQL background processes? for more information on the background processes that Postgres starts or this example processlist in the manual

This presentation also gives some insight about the Postgres background processes.