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From the slow query log of holbach:

# Query_time: 1  Lock_time: 0  Rows_sent: 50  Rows_examined: 
28229
SELECT log_type, log_action, log_timestamp,
                        log_user, user_name,
                        log_namespace, log_title, cur_id,
                        log_comment, log_params FROM `user`, 
`logging` LEFT OUTER JOIN `cur` ON 
log_namespace=cur_namespace AND log_title=cur_title WHERE 
user_id=log_user ORDER BY log_timestamp DESC  LIMIT 0,50;

The explain:

explain SELECT log_type, log_action, log_timestamp,
    ->                         log_user, user_name,
    ->                         log_namespace, log_title, 
cur_id,
    ->                         log_comment, log_params FROM 
`user`, `logging` LEFT OUTER JOIN `cur` ON 
log_namespace=cur_namespace AND log_title=cur_title WHERE 
user_id=log_user ORDER BY log_timestamp DESC  LIMIT 0,50\G
*************************** 1. row 
***************************
        table: logging
         type: ALL
possible_keys: user_time
          key: NULL
      key_len: NULL
          ref: NULL
         rows: 27972
        Extra: Using filesort
*************************** 2. row 
***************************
        table: user
         type: eq_ref
possible_keys: user_id
          key: user_id
      key_len: 4
          ref: logging.log_user
         rows: 1
        Extra:
*************************** 3. row 
***************************
        table: cur
         type: ref
possible_keys: cur_title,name_title_timestamp
          key: cur_title
      key_len: 255
          ref: logging.log_title
         rows: 1
        Extra:

Note the type: ALL for the logging table and the Extra: 
Using filesort as well as the estimated 27972 rows. It's 
doing a full table scan because there's no index which lets 
it get the records in timestamp order.

I suggest adding an index log_timestamp (log_timestamp) .

Assuming that makes sense, let me know and I'll put it live 
on the Wikimedia servers next low load time.

It's also using the wrong index for cur but that may clear 
up after this change.