Starting with the daemon process

The first process that is started when we start PostgreSQL is /usr/local/pgsql/bin/postgres. This process has quite a few responsibilities such as performing recovery, initializing shared data structures/memory space, and kicking off the mandatory and optional processes. These processes are also referred to as utility processes and include bgwriter, checkpointer, autovacuum launcher, log writer, stats collector process, and so on. The daemon process also listens for connection requests, receives requests for connections from clients, and spawns server processes for the client. It's obvious that the daemon itself is a mandatory process that should be running for a user to connect to the database.

Let's focus on the user connecting-issuing-commands scenario and other pieces should fall in place. The following diagram walks you through the process of how the daemon process receives a connection request and starts (forks) a backend process. The backend...