18.5. Shutting Down the Server
There are several ways to shut down the database server. You control
the type of shutdown by sending different signals to the master
postgres
process.
- SIGTERM
-
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 If the server is in online backup mode, it additionally waits until online backup mode is no longer active. While backup mode is active, new connections will still be allowed, but only to superusers (this exception allows a superuser to connect to terminate online backup mode). 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.
- SIGINT
-
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. If the server is in online backup mode, backup mode will be terminated, rendering the backup useless.
- SIGQUIT
-
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 master 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`
Important
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 9.83
) or send a
SIGTERM
signal to the child process associated with
the session.