Yesterday I wrote:
> * On successful completion, the cutoff XID is stored in
> pg_class.relvacuumxid, and pg_database.datvacuumxid is updated
> if appropriate.  (The minxid columns are now useless, but unless there
> is another reason to force initdb before 8.2, I'm inclined to leave them
> there and unused.  We can remove 'em in 8.3.)

After a closer look I am thinking that maybe we should go ahead and
replace relvacuumxid/relminxid and datvacuumxid/datminxid by single
columns named relfrozenxid and datfrozenxid respectively.  The reason
is that our documentation has for a long time recommended

        SELECT datname, age(datfrozenxid) FROM pg_database;

as a good way to check for databases approaching wraparound.
(In fact it still does ... apparently Alvaro didn't bother to update 
maintenance.sgml when he redid that code.)

I don't know how many people might have such queries embedded in
maintenance scripts, but any who do will find their scripts broken by
8.2 as it now stands.  Which is a bit silly considering that the
proposed patch will be maintaining a column having exactly the
longstanding definition of datfrozenxid:

       All rows inserted by transaction IDs before this one have been
       relabeled with a permanent (<quote>frozen</>) transaction ID in this

I prefer to avoid forcing initdb in late beta, because it causes extra
work for our long-suffering beta testers, but at the moment I'm thinking
this is worth fixing now rather than later.  Comments?

                        regards, tom lane

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