Wikimedia Bugzilla is closed!

Lately, the DB has required several tens of seconds to supply the results of a query that took about 2 seconds in the past.

Here's an example:
                            [1] => Array
                                (
                                    [time] => 18.95
                                    [query] => SELECT rev_timestamp, page_title, page_namespace FROM revision_userindex JOIN page ON page_id = rev_page WHERE (`rev_user` = '14836860') AND `rev_timestamp` > 1 ORDER BY rev_timestamp ASC LIMIT 0,2688354;
                                    [result] => succeeded
                                )