There are several ways to shut down the database server.
Under the hood, they all reduce to sending a signal to the supervisor
postgres process.
If you are using a pre-packaged version of PostgreSQL, and you used its provisions for starting the server, then you should also use its provisions for stopping the server. Consult the package-level documentation for details.
When managing the server directly, you can control the type of shutdown
by sending different signals to the postgres
process:
This is the Smart Shutdown mode. After receiving SIGTERM, the server disallows new connections, but lets existing sessions end their work normally. It shuts down only after all of the sessions terminate. If the server is in recovery when a smart shutdown is requested, recovery and streaming replication will be stopped only after all regular sessions have terminated.
This is the Fast Shutdown mode. The server disallows new connections and sends all existing server processes SIGTERM, which will cause them to abort their current transactions and exit promptly. It then waits for all server processes to exit and finally shuts down.
This is the Immediate Shutdown mode. The server will send SIGQUIT to all child processes and wait for them to terminate. If any do not terminate within 5 seconds, they will be sent SIGKILL. The supervisor server process exits as soon as all child processes have exited, without doing normal database shutdown processing. This will lead to recovery (by replaying the WAL log) upon next start-up. This is recommended only in emergencies.
The pg_ctl program provides a convenient
interface for sending these signals to shut down the server.
Alternatively, you can send the signal directly using kill
on non-Windows systems.
The PID of the postgres process can be
found using the ps program, or from the file
postmaster.pid in the data directory. For
example, to do a fast shutdown:
$ kill -INT `head -1 /usr/local/pgsql/data/postmaster.pid`
It is best not to use SIGKILL to shut down the
server. Doing so will prevent the server from releasing shared memory and
semaphores. Furthermore, SIGKILL kills
the postgres process without letting it relay the
signal to its subprocesses, so it might be necessary to kill the
individual subprocesses by hand as well.
To terminate an individual session while allowing other sessions to
continue, use pg_terminate_backend() (see Table 9.90) or send a
SIGTERM signal to the child process associated with
the session.