Freezing without cleanup lock

While warning a client that just did a Slony-based version upgrade to 
make sure to freeze the new database, it occurred to me that it should 
be safe to freeze without the cleanup lock. This is interesting because 
it would allow a scan_all vacuum to do it's job without blocking on the 
cleanup lock.

Does anyone have a feel for whether scan_all vacuums blocking on the 
cleanup lock is an actual problem?
-- 
Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX
Experts in Analytics, Data Architecture and PostgreSQL
Data in Trouble? Get it in Treble! http://BlueTreble.com