On 2/5/08, Tim Starling tstarling@wikimedia.org wrote:
Another way to find a previous revision is to order by rev_id. But rev_id is not monotonic with respect to time, due to various accidents of history. There are step discontinuities, such as those introduced by undeletion or the conversion script. It is however used by the older/newer links on the old revision views. This algorithm is chosen over the timestamp algorithm because at the time the revision is fetched, the timestamp is not known, only the rev_id is known. Finding out the timestamp would require an extra query.
I'm guessing a one-time re-assignment of rev_id's for edits older than [timestamp of most recent discontinuity] is out of the question :-)
—C.W.