/*
 * pg_ctl uses SIGTERM, SIGINT and SIGQUIT to request different types of
 * shutdown.
 */
static void
handle_pm_shutdown_request_signal(SIGNAL_ARGS)
{
	switch (postgres_signal_arg)
	{
		case SIGTERM:
			/* smart is implied if the other two flags aren't set */
			pending_pm_shutdown_request = true;
			break;
		case SIGINT:
			pending_pm_fast_shutdown_request = true;
			pending_pm_shutdown_request = true;
			break;
		case SIGQUIT:
			pending_pm_immediate_shutdown_request = true;
			pending_pm_shutdown_request = true;
			break;
	}
	SetLatch(MyLatch);
}
…
	switch (mode)
	{
		case SmartShutdown:

			/*
			 * Smart Shutdown:
			 *
			 * Wait for children to end their work, then shut down.
			 */
			if (Shutdown >= SmartShutdown)
				break;
			Shutdown = SmartShutdown;
			ereport(LOG,
					(errmsg("received smart shutdown request")));
…
		case FastShutdown:

			/*
			 * Fast Shutdown:
			 *
			 * Abort all children with SIGTERM (rollback active transactions
			 * and exit) and shut down when they are gone.
			 */
			if (Shutdown >= FastShutdown)
				break;
			Shutdown = FastShutdown;
			ereport(LOG,
					(errmsg("received fast shutdown request")));

Warm-up