proposal: LISTEN *

Hi,

I've in the past wanted to listen on all notification channels in the
current database for debugging purposes. But recently I came across
another use case. Since having multiple postgres backends listening for
notifications is very inefficient (one Thursday I found out 30% of our
CPU time was spent spinning on s_locks around the notification code), it
makes sense to implement a notification server of sorts which then
passes on notifications from postgres to interested clients. A server
like this would be a lot more simple to implement if there was a way to
announce that the client wants to see all notifications, regardless of
the name of the channel.

Attached is a very crude proof-of-concept patch implementing this. Any
thoughts on the idea?

.m