It would be nice if Quarry users could find out what plan the database server is using to execute their queries. This should be possible with the [[http://s.petrunia.net/blog/?p=89|SHOW EXPLAIN]] functionality in MariaDB. SHOW EXPLAIN works by describing the plan of an actively executing query, so it can describe plans that traverse views.
The ideal implementation would probably be to automatically run SHOW EXPLAIN on all queries and store the result in parallel with the query output so that the user doesn't have to hit an "explain" button at just the right time to get results. An alternative solution would be to add a checkbox for "explain" near the "submit query" button.