VACUUM and transactions in different databases

[Cornelia Boenigk <c@xxxxxxxxxxxxxxxxxxx>]

Hi all

If I have a running transaction in database1 and try to vacuum database2 
but the dead tuples in database2 cannot be removed.

INFO:  vacuuming "public.dummy1"
INFO:  "dummy1": found 0 removable, 140000 nonremovable row versions in 
1341 pages
DETAIL:  135000 dead row versions cannot be removed yet.

How can I achieve that database2 is vacuumed while a transaction in 
database1 is not yet commited?

Regards
conni