In the talk show view, the current user is being used in the cache key. I believe this is only used for caching whether a talk is cached or not. This increases the stored cache significantly as a _talk has to be cached for every user who views it. Instead it should use a boolean value to indicate if the talk is watched or not in order for the partial to be cached and shared amongst users.

https://github.com/adrienpoly/rubyvideo/blob/20b2b1a57b6fd823f3c16f6484d877b58e2b56e0/app/views/talks/show.html.erb#L17