Querying by rev_actor is very slow on the Toolforge replicas.
SELECT * FROM `enwiki_p`.`revision_userindex` WHERE rev_actor = 7528 LIMIT 1
Meanwhile archive seems to have the necessary indexing:
SELECT * FROM `enwiki_p`.`archive_userindex` WHERE ar_actor = 7528 LIMIT 1
I assume this was an oversight. We can of course use rev_user, which does have indexing, but this would only work for registered users.