In PBFT view change what happens to committed operations after a valid snapshot

Question

PBFT says that if the timer of backup i expires in view v then it starts a view change for v+1 by multicasting <view-change, v+1, n, C, P, i> where n is the sequence number of the last stable checkpoint s and P is a set containing a set Pm for each request m that prepared at i with a sequence number higher than n. 

Now, the checkpoints are taken periodically so, there can be prepared messages at i with a sequence number higher than n which are already committed. We don't want these to be included in Pm as they are already committed. So, how does PBFT handles that?

Answer 1

I think that those messages are executed again. When a view-change happens, all the nodes would be in the same checkpoint. When the "new" primary for the view v + 1 receives 2⨍ valid view-change messages, multicasts a new-view message. 

In the message that is sent, it indicates: V: set of received and valid view-change messages. P: set of pre-prepared unprocessed messages. These messages are calculate as follows: From the last stable checkpoint, you get the sequence number of the last executed request. This value will correspond to the min-s. Take the largest sequence number of all prepared messages you have received. 

This value will correspond to the max-s. As a result, it generates as many pre-prepared messages as needed. Each node saves the log of the messages that are not inside a chekcpoint, so they don't need to be procesed again.