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.
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.