https://bugzilla.wikimedia.org/show_bug.cgi?id=40870

--- Comment #1 from Sam Reed (reedy) <[email protected]> 2012-10-08 20:55:49 
UTC ---
I thought this might've been a dupe...

Either way, it's not a nice query

mysql> EXPLAIN SELECT img_name, img_size FROM categorylinks, page, image WHERE
cl_from=page_id AND cl_to = 'Astronomy' AND page_title = img_name ORDER BY
img_size;
+----+-------------+---------------+--------+---------------------------------+--------------+---------+-----------------------------------+------+-----------------------------------------------------------+
| id | select_type | table         | type   | possible_keys                   |
key          | key_len | ref                               | rows | Extra      
                                              |
+----+-------------+---------------+--------+---------------------------------+--------------+---------+-----------------------------------+------+-----------------------------------------------------------+
|  1 | SIMPLE      | categorylinks | ref    | cl_from,cl_timestamp,cl_sortkey |
cl_timestamp | 257     | const                             |  227 | Using
where; Using index; Using temporary; Using filesort |
|  1 | SIMPLE      | page          | eq_ref | PRIMARY                         |
PRIMARY      | 4       | commonswiki.categorylinks.cl_from |    1 |            
                                              |
|  1 | SIMPLE      | image         | eq_ref | PRIMARY                         |
PRIMARY      | 257     | commonswiki.page.page_title       |    1 |            
                                              |
+----+-------------+---------------+--------+---------------------------------+--------------+---------+-----------------------------------+------+-----------------------------------------------------------+
3 rows in set (0.00 sec)

mysql> EXPLAIN SELECT img_name, img_size FROM categorylinks FORCE INDEX
(cl_from), page, image WHERE cl_from=page_id AND cl_to = 'Astronomy' AND
page_title = img_name ORDER BY img_size;
+----+-------------+---------------+--------+---------------+------------+---------+--------------------------------+----------+----------------------------------------------+
| id | select_type | table         | type   | possible_keys | key        |
key_len | ref                            | rows     | Extra                    
                   |
+----+-------------+---------------+--------+---------------+------------+---------+--------------------------------+----------+----------------------------------------------+
|  1 | SIMPLE      | page          | index  | PRIMARY       | name_title | 261 
   | NULL                           | 19081712 | Using index; Using temporary;
Using filesort |
|  1 | SIMPLE      | image         | eq_ref | PRIMARY       | PRIMARY    | 257 
   | commonswiki.page.page_title    |        1 |                               
              |
|  1 | SIMPLE      | categorylinks | eq_ref | cl_from       | cl_from    | 261 
   | commonswiki.page.page_id,const |        1 | Using where; Using index      
              |
+----+-------------+---------------+--------+---------------+------------+---------+--------------------------------+----------+----------------------------------------------+
3 rows in set (0.00 sec)


http://p.defau.lt/?c8nPdSZVr7MLORs00CQB9w

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