In es 7.6, I see that we introduced persisted local checkpoint and processed local checkpoint. After each update replication, replicas return their persisted local checkpoint to primary shard. And based on these checkpoints from in-sync replicas, primary would advance the global check point. However, since persisted local checkpoint could lag behind the op seq that's really processed(namely processed local checkpoint)，I wonder is it possible for the global checkpoint to catch up to MAX_SEQ.
Here I given an example to illustrate this. Suppose we have 3 copies for one shard (suppose all copies have inital seq no 6 for both persisted and processed local checkpoint). And after replicating an update, we could have:
Primary : persisted local checkpoint is 6, processed local checkpoint 7
Replica1: persisted local checkpoint is 6, processed local checkpoint 7
Replica2: persisted local checkpoint is 6, processed local checkpoint 7
For the moment, the global checkpoint doesn't advance and it lags behind MAX_SEQ 7。I don't see when the global checkpoint would catch up to MAX_SEQ.