If a notify is sent and then PG is immediately shut down, wouldn't PG want to save that message for processing after startup?
Or is the message just discarded?
Adrian gave details but trying to figure out notification semantics across a system reboot seems like a headache for little benefit.
Its likely assumed that upon first connection the client would eagerly load the relevant data - capturing the static state of the system at that time - and then only perform additional queries upon notification.