On Oct21, 2011, at 19:09 , Tom Lane wrote: > Florian Pflug <f...@phlo.org> writes: >> On Oct21, 2011, at 17:36 , Tom Lane wrote: >>> 3. Remove the optimization that lets GetOldestXmin ignore XIDs outside >>> the current database. This sounds bad, but OTOH I don't think there's >>> ever been any proof that this optimization is worth much in real-world >>> usage. We've already had to lobotomize that optimization for walsender >>> processes, anyway. > >> Hm, we've told people who wanted cross-database access to tables in the >> past to either > >> * use dblink or > >> * not split their tables over multiple databases in the first place, >> and to use schemas instead > >> If we remove the GetOldestXmin optimization, we're essentially reversing >> course on this. Do we really wanna go there? > > Huh? The behavior of GetOldestXmin is purely a backend-internal matter. > I don't see how it's related to cross-database access --- or at least, > changing this would not represent a significant move towards supporting > that.
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. best regards, Florian Pflug -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
