Previous commits (maybe from the commit f45a163eb8a4248a59c7cd70488cd72a5f5d2c7d) has serious performance problem, when the row of "taggable" table is much larger then subqueries of "tagging" table.
In this case (in addition, tables has the properly indexes), in circumstance of performances, we should use `INNER JOIN` wish subqueries, instead of `IN` query...
I'd quick fix the problem, by using `EXISTS` query, But it still slow down with the huge "taggable" table.