Thanks for the feedback David Jacot David Jacot wrote: > I have one question regarding how fetch from followers will > work when the leader is recovering. My understanding is that > the leader will reject any produce and fetch requests with a > NOT_LEADER_OR_FOLLOWER error while the followers > will fence any fetch requests based on the incremented leader > epoch. That seems OK for recent consumers from a correctness > perspective but it might be a little weird for older consumers which > do not set the leader epoch in the fetch request (prior to v9). They > would be able to fetch from the followers while the leader recovers > if I understand it correctly. It might be good to clarify this case in > the KIP. What do you think?
The leader will return a NOT_LEADER_OR_FOLLOWER error on the FETCH response if the leader is still recovering. This is true even if all other FETCH requests validation success. Looking at the history of the Errors type, the error NOT_LEADER_OR_FOLLOWER(6) has always existed so all client versions should be able to handle it: https://github.com/apache/kafka/blob/fa6339c19cd06880d32ec9a5ee6b66e7f1488dcf/clients/src/main/java/org/apache/kafka/common/protocol/Errors.java#L35 Does that address your concern David? Thanks -José
