> If you render the view without any cache with 10 things then you'd perform 20 queries but after the cache is warm you'd perform 0 queries. If item 5's Y gets updated then you only need to bust the cache for item 5 and query only item 5's Y association. Performing a preloaded query to get all X 10 things with their Y associated things could be an expensive query.

The technique you describe makes sense, but how often is that preload query actually that expensive? Usually if I see an expensive query in Rails, it's because either 1) the indexes are missing for the joins or 2) you're instantiating extra full-blown objects when only some tiny amount of data of a primitive type is required.

This kind of stuff is a good opportunity to just write the query directly that gets the data you really do need, rather than relying on the ORM and its overhead.

If the problem is "maybe the user will want to see this, maybe they won't" then in many cases the easiest win is to lazy load the more detailed view with a new query that is only fired on some user interaction.