We've noticed that the heavy use of NOTIFY by Slony-I means that there
are Plenty O Dead Tuples in the system table pg_listener.

For now, we're vacuuming it fairly voraciously in our local "regular
maintenance regimen."  It's more than likely that this should be
rolled into the regular vacuums done by the slon engines.  I'll see if
I can make up a patch for CVS head...
-- 
"cbbrowne","@","ca.afilias.info"
<http://dev6.int.libertyrms.com/>
Christopher Browne
(416) 673-4124 (land)