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Special:Ancientpages has a field "UNIX_TIMESTAMP(cur_timestamp) as value" and
orders by "value". There is no value field in the database so the cur_timestamp
indec in cur can't be used. unix_timestamp and cur_timestamp appear to have the
same order so the query should be changed to order by cur_timestamp insted of by
value. Change from:

EXPLAIN SELECT 'Ancientpages' as type, cur_namespace as namespace, cur_title as
title, UNIX_TIMESTAMP(cur_timestamp) as value FROM cur USE INDEX (cur_timestamp)
WHERE cur_namespace=0 AND cur_is_redirect=0 ORDER BY value LIMIT 1350,250:

*** row 1 ***
          table:  cur
           type:  ALL
  possible_keys:  NULL
            key:  NULL
        key_len:  NULL
            ref:  NULL
           rows:  382867
          Extra:  Using where; Using filesort

To:

EXPLAIN SELECT 'Ancientpages' as type, cur_namespace as namespace, cur_title as
title, UNIX_TIMESTAMP(cur_timestamp) as value FROM cur USE INDEX (cur_timestamp)
WHERE cur_namespace=0 AND cur_is_redirect=0 ORDER BY cur_timestamp LIMIT 1350,250:

*** row 1 ***
          table:  cur
           type:  index
  possible_keys:  NULL
            key:  cur_timestamp
        key_len:  14
            ref:  NULL
           rows:  280120
          Extra:  Using where;

No filesort this time - the key is now being used. This avoids the need to scan
all of cur.