Michael Meskes <meskes(at)postgresql(dot)org> writes:
> A customer's machine hangs from time to time. All we could find so far is
> that postgres seems to be in state "idle in transaction":
You evidently have some client applications holding open transactions
that have locks on some tables. That's not a deadlock --- at least,
it's not Postgres' fault. The VACUUM is waiting to get exclusive access
to some table that's held by one of these clients, and the COPY is
probably queued up behind the VACUUM.
regards, tom lane