Cache most frequently used keys on the client

Background
When a Couchbase Server node is starting up, it creates any database files that are necessary and begins serving data immediately. However, if there is already data on the disk, the node needs to read all of this data from the disk before it can begin serving data. This process is called warmup. One of the tasks performed during warmup is loading keys into memory.

Problem
Clients need to read these keys over the network.

Request
Cache most frequently used keys on the client side:

• fetch the keys that are loaded into memory on the server side during warmup, and bring them into memory on the client (in order to reduce network impact later on)
• update the client cache as hot keys change on the server end