Read-your-writes consistency guarantee for relaxed reads

[penberg]

With relaxed reads, there's currently no guarantee on read-your-write consistency. This is because a write will be acknowledged when the write is applied to the state machine of the leader, but not on the local replica.

Example:

• A follower node F receives a write request, which is delegated to node L, which is the leader.
• The write is replicated to the logs of all nodes (but not necessarily applied).
• The write is applied to the state machine of L.
• L acknowledges the write to F and F acknowledges the write to the client.
• A relaxed read request arrives on node F, which does not yet have the write applied to its state machine, violating read-your-writes consistency.