POE::Component::MessageQueue::Storage::Double -- Stores composed of two other stores.
Refactor mercilessly, as they say. They also say don't repeat yourself. This module contains functionality for any store that is a composition of two stores. At least Throttled and Complex share this trait, and it doesn't make any sense to duplicate code between them.
Takes a reference to a storage engine to use as the front store / back store.
This isn't implemented because Complex and Throttled differ here. Perhaps your storage differs here as well. This is essentially where you specify policy about what goes in which store. Be sure you update the front_info hash when you store something!
And this is where you specify policy about what happens when you die. You lucky person, you.