It's an edge case, it only happens _if_ you have either very long running transactions holding xids, or you haven't vacuumed your database enough and it has to

It's an edge case, it only happens _if_ you have either very long running transactions holding xids, or you haven't vacuumed your database enough and it has to do a blocking vacuum to move the xid forward far enough to wrap around. Most postgres databases wrap around with no issues. The problem with increasing the size is a pair of xids are needed for every row, so you're doubling that if you go to 64 bits.