Persistence using LRU eviction

[SimonRichardson]

Potentially it is possible to have a level of persistence when the LRU causes an eviction based on size. If a bucket with in the LRU states that a size eviction has happened, we could store that in a WAL or similar. This almost comes for free, there are areas that need more thought:

1. Searching with in the persisted data once it has been written to disk
2. Potential convergence on persisted data; if writing to a central location, then how do we know what should be added/removed because LRU eviction can happen out of order across nodes, so consensus can be wrong. Maybe a convergence is never achieved?