"Carlos H. Reimer" <carlosreimer@xxxxxxxxxxxx> writes: > I would like to understand better the logic to determine when a xid is older > than another one. It's circular mod 2^32, with a special case for FrozenXID. It's a mistake to imagine that XIDs are unsigned ints, really --- the comparison doesn't work that way. For an XID of say 1billion, XIDs from 1billion to 3billion are "after", the rest "before". So once a row is created, it has to be deleted or frozen within 2 billion transactions, else its XID wraps around and appears to be "in the future" rather than "in the past" compared to current XIDs. regards, tom lane
