Right now UserMerge::mergeUser() updates ID fields (e.g., ar_user) and text fields (e.g., ar_user_text) in separate queries. Considering ar_user and ar_user_text should be exactly the same for a logged in user, you could cut the number of DB queries in half by combining them. For large wikis, this may save a significant amount of time since it doesn't have to scan each table twice.
Version: unspecified
Severity: enhancement