Re: relfrozenxid may disagree with row XIDs after 1ccc1e05ae

One option is to add the logic in fix_hang_15.patch to master as well
(always remove tuples older than OldestXmin). This addresses your
concern about gaining confidence in a single solution.

However, I can see how removing more tuples could be concerning. In
the case that the horizon moves backwards because of a standby
reconnecting, I think the worst case is that removing that tuple
causes a recovery conflict on the standby (depending on the value of
max_standby_streaming_delay et al).

/*
 * OldestXmin is the Xid below which tuples deleted by any xact (that
 * committed) should be considered DEAD, not just RECENTLY_DEAD.