Autovacuums running on unused tables/databases

I am having some issues with forced autovacuum kicking on and vacuuming tables that should not need to be vacuum'd. Initially we believed this to just be high usage on these tables and dug into what could be causing xid's to increase so quickly. We were never able to find querys that were doing this. Now I have seen autovacuum running on a database that had been marked for deletion a week prior. (Once a database in our system has been marked for deletion all access from our applications are blocked to it). Just to be clear though, we currently have a system set up to vacuum tables on the weekends and smaller tables every night. Autovacuum is disabled and the ones that are kicking on are forced to prevent xid rollover.

For our custom vacuum scripts we are using relfrozenid with a query similar to what is mentioned in the postgres docs.

SELECT relname, age(relfrozenxid) FROM pg_class WHERE relkind = 'r';
SELECT datname, age(datfrozenxid) FROM pg_database;

After creating a new database however and watching the xid's on a particular table we can see that they grow even though nothing is accessing them. Vacuuming them returns them back down but they continue growing.

We are currently running postgres 8.3.10

Any help as to why the xid's seem to be growing out of control would be very appreciated.

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