Re: Change behavior of (m)xid_age

On Wed, Oct 21, 2015 at 1:33 PM, Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com> wrote:
> Currently, xid_age() returns INT_MAX for a permanent xid. The comment in the
> function that 'Permanent XIDs are always infinitely old' may be technically
> correct, but returning INT_MAX is a useless behavior because it actually
> makes it look like that XID is in immediate wraparound danger. I think we
> should change it to return either 0, -1, or INT_MIN. To me, 0 makes the most
> sense for monitoring relfrozenxid.

As far as I know, relfrozenxid is only a permanent XID for relkinds
that don't have storage; then it's zero. So I think you should just
change your query to ignore pg_class rows where relfrozenxid = 0, and
leave xid_age() alone.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company