Florian Pflug <fgp(at)phlo(dot)org> writes:
> AFAIR, the performance hit we'd take by making the vacuum cutoff point
> (i.e. GetOldestXmin()) global instead of database-local has been repeatedly
> used in the past as an against against cross-database queries. I have to
> admit that I currently cannot seem to find an entry in the archives to
> back that up, though.
To my mind, the main problem with cross-database queries is that none of
the backend is set up to deal with more than one set of system catalogs.
regards, tom lane