Trying to speed up user_block's block #2 (Who's New) which currently uses a query that needs a filesort. Although the "status" column can only be 0 or 1, the query is expressed as status != 0 -- I think someone expects the status column to have more possible values in the future.

ALTER TABLE drupal_users ADD KEY user_block_2(created, status, access);

helps a lot with small numbers of rows. By using an index scan which gets cut off by the range, it reduces query time from around 15-17ms to .5--.6ms on my desktop machine. However, mysql doesn't realize that it should use that index without a hint, which defeats my goal of not having to maintain yet another patch on top of drupal.

If modifying drupal code doesn't bother you, you can try adding the above index and changing the user block query to:

SELECT uid, name FROM {users} USE INDEX(user_block_2) WHERE status != 0 AND access != 0 ORDER BY created DESC