view the remining # of TX ID's available per db (before TX ID wraparound failure)

Hi all;

I want to be sure we know exactly how close we are to a tx id wraparound
failure.

I ran this:

select datname, age(datfrozenxid) from pg_database;

I assume the resulting value is the number of available tx id's left per db,
is this correct?

Also is there a way in 8.3 to determine which tables need to be vacuum'ed so
PostgreSQL can reset the tx id values?

Thanks in advance...