How to track down locks held by recovery process on a slave?

Hi there,

I am using a postgres 9.2 slave for some reports and I noticed that
sometimes they are held up because certain activity on the master like
vacuums can affect long queries on a slave .

Looking at pg_locks view , I can see that the recovering process on the
slave is holding some AccessExclusiveLock locks on relations which numbers
that do not mach any pg_class.oid.

Any idea How could I find out which relations are locked by the recovering
process?

Thanks in advance,
A.A.