Anyone seen this kind of lock pileup?

All,

Having an interesting issue on one 8.4 database.  Due to poor 
application design, the application is requesting 8-15 exclusive 
(update) locks on the same row on parallel connections pretty much 
simultaneously (i.e. < 50ms apart).

What's odd about this is that the resulting "lock pileup" takes a 
mysterious 2-3.5 seconds to clear, despite the fact that none of the 
connections are *doing* anything during that time, nor are there 
deadlock errors.  In theory at least, the locks should clear out in 
reverse order in less than a second; none of the individual statements 
takes more than 10ms to execute.

Has anyone else seen something like this?  Any idea what causes it?

-- 
                                   -- Josh Berkus
                                      PostgreSQL Experts Inc.
                                      http://www.pgexperts.com