+ # Find the id of the last snapshot to be created. This is used for
+ # measuring time in a way: we record this value in each segment we
+ # expire on this run, and then on a future run can tell if there have
+ # been intervening backups made.
+ cur.execute("select max(snapshotid) from snapshots")
+ last_snapshotid = cur.fetchone()[0]
+