Why does PostgreSQL have so many processes, even when idle?
As noted in the answer above, PostgreSQL is process based, so it starts one postgres (or postgres.exe on Windows) instance per connection. The postmaster (which accepts connections and starts new postgres instances for them) is always running. In addition, PostgreSQL generally has one or more “helper” processes like the stats collector, background writer, autovacuum daemon, walsender, etc, all of which show up as “postgres” instances in most system monitoring tools. Despite the number of processes, they actually use very little in the way of real resources. See the next answer.
