-- 1) ran fine for 2 mi records table.
-- 2) assuming the table name is clients.

select did, cid, did - cid as gap
from
(
  select
  d.id as did,
  (select min(id) as cid from clients c where c.id > d.id  ) as cid
  from
  clients d
) as t
order by gap asc
limit 10