postgres process got stuck in "notify interrupt waiting" status

Hi.

We use LISTEN/NOTIFY quite a bit but today something unusual (bad) happened.

Number of processes waiting for a lock just started to go up up up.

I finally found the object being locked was pg_listener which
RhodiumToad on IRC kindly informed happens during LISTEN/NOTIFY. The
process that had the lock (in pg_locks it had granted = t ) was shown
by ps in status "notify interrupt waiting" and has had the lock for
over half an hour. (Usually these notifications are very quick.)

the process would not respond to kill, so I kill -9'ed

The only reference I could find to a similar problem was at
http://archives.postgresql.org/pgsql-performance/2008-02/msg00345.php
which seemed to indicate a process should not be in this state for
very long.

We are on postgres 8.4.12.

I'd like to figure out what happened.

There is a web server that talks to this database server (amongst
other clients), and the client addr and port mapped to this web
server, but there was no process on the web server matching the port
number. that's when I decided to kill the postgres process.

Anything I should know or read up on? Any suggestions?

I'd like the system to be able to recover, and for the process to
terminate if the client is no longer around.

Best,
Aleksey