I've submitted a couple of patches in Ligththouse.
Provide NoStore implementation of ActiveSupport::Cache::Store
This patch provides a NoStore implementation of ActiveSupport::Cache::Store suitable for use in development and test environments where the code need to use the cache interface, but actually caching data is not desired.
https://rails.lighthouseapp.com/projects/8994-ruby-on-rails/tickets/6128
Reduce memory bloat in ActiveRecord transactions
This patch reduces memory bloat in ActiveRecord transactions. With the introduction after_commit and after_rollback callbacks references are kept to all records updated in a transaction until the transaction completes. This can lead to memory bloat with large transactions.
The code change replaces the references to weak references unless the objects implement these callbacks. This allows the garbage collector to reclaim objects that won't be executing a callback.
https://rails.lighthouseapp.com/projects/8994-ruby-on-rails/tickets/6129