If the query was expensive and could be run periodically, I'd either create a materialized view that gets refreshed as often as necessary (maybe by https://dockyard.com/blog/2017/11/29/need-an-elixir-dependen...) or use a GenServer process for caching that data (as you might do with Redis otherwise).

I don't think the view rendering itself would ever be a performance issue, but rendering a view is just a function call in Phoenix, so I could take a similar approach there - store it in a GenServer.