-- Crossposting to pgsql-hackers --

Jan Wieck wrote:

> 
> For the record,
> 
> Slony-I uses a pg_listener entry as a locking mechanism to prevent 
> multiple concurrent slon processes serving the same node. The function 
> Async_Unlisten() is used in a backend function that is called during 
> slon startup in an attempt to remove stale pg_listener entries left over 
> from a PostgreSQL crash. This function scans pg_listener, tries to 
> kill(pid, 0) the backends listed in there in order to check if they are 
> alive and if not, calls Async_Unlisten() _with that foreign pid_.
> 
> This means, that the very functionality we use is gone. What we have to 
> find out is if we still need that functionality, or if something else in 
> 8.1 does the cleanup for us during postmaster restart already, so that 
> we can skip the whole thing.

Just tried it: LISTEN something, sudo killall -9 postmaster, and after 
restart the pg_listener entry was still there.
So postmaster doesn't clean up pg_listener, is slon supposed to do that 
with a DELETE FROM pg_listener?

Regards,
Andreas