MultiXactMemberControlLock contention on a replica

[Christophe Pettus]

On a whole fleet of load-balanced replicas, we saw an incident where one 
particular query started backing up on MultiXactMemberControlLock and 
multixact_member.  There was no sign of this backup on the primary.  Under what 
conditions would there be enough multixact members on a replica (where you 
can't do UPDATE / SELECT FOR UPDATE / FOR SHARE) to start spilling to disk?
--
-- Christophe Pettus
   x...@thebuild.com