THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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For LeaderAndISRCommand: it calls on_LeaderAndISRCommand(). on_LeaderAndISRCommand(command): 1. Read the set of partitions set_P from command. 2. For each partition P in set_p 2.0 if P doesn't exist locally, call startReplica() 2.1 If the command asks this broker to be the new leader for P and this broker is not already the leader for P, 2.1.1 call becomeLeader() 2.2 If the command asks this broker to following a leader L and the broker is not already following L 2.2.1 call becomeFollower() 3. If the command has a flag INIT, delete all local partitions not in set_p. becomeLeader(r: Replica, command) { stop the ReplicaFetcherThread to the old leader //after this, no more messages from the old leader can be appended to r r.leaderAndISRZKVersion = command.leaderAndISRZKVersion r.ISR = command.ISR stop the HW checkpoint thread for r r.isLeader = true //enables reads/writes to this partition on this broker r.LeaderAndISRVersionInZK = command.LeaderAndISRVersionInZK start a commit thread on r } Note that the new leader's HW could be behind the HW of the previous leader. Therefore, immediately after the leadership transition, it is possible for a consumer (client) to ask for an offset larger than the new leader's HW. To handle this case, if the consumer is asking for an offset between the leader's HW and LEO, the broker could just return an empty set. If the requested offset is larger than LEO, the broker would still return OffsetOutofRangeException. becomeFollower(r: Replica) { stop the ReplicaFetcherThread to the old leader r.isLeader = false //disables reads/writes to this partition on this broker stop the commit thread, if any truncate the log to r.hw start a new ReplicaFetcherThread to the current leader of r, from offset r.leo } startReplica(r: Replica) { create the partition directory locally, if not present start the HW checkpoint thread for r } For StopReplicaCommand: it calls on_StopReplicaCommand(). on_StopReplicaCommand(command): 1. Read the list of partitions from command. 2. For each such partition P 2.1 call stopReplica() on p stopReplica(r: Replica) { stop the ReplicaFetcherThread associated with r, if any. stop the HW checkpoint thread for r delete the partition directory locally, if present } |
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ReplicaFetchReqeust { topic: String partition_id: Int replica_id: Int offset: Long } ReplicaFetchResponse { hw: Long // the offset of the last message committed at the leader messages: MessageSet // fetched messages } At the leader, on receiving a ReplicaFetchRequest, it calls on_ReplicaFetchRequest on_ReplicaFetchRequest(f: ReplicaFetchRequest) { leader = getLeaderReplica(f.topic, f.partition_id) if(leader == null) throw NotLeaderException response = new ReplicaFetcherResponse getReplica(f.topic, f.partition_id, f.replica_id).leo = f.offset call maybe_change_ISR() // see if we need to shrink or expand ISR leader.hw = min of leo of every replica in ISR // try to advance HW // trigger potential acks to produce requests response.messages = fetch messages starting from f.offset from leader.log response.hw = leader.hw send response back } maybe_change_ISR() { // If a follower is slow or is not active at all, the leader will want to take it out of ISR so that it can commit messages // with fewer replicas. find the smallest leo (leo_min) of every replica in ISR if ( leader.leo - leo_min > MAX_BYTES_LAG || the replica with leo_min hasn't updated leo for more than MAX_TIME_LAG) newISR = ISR - replica with leo_min // If a follower has fully caught up, the leader will want to add it to ISR. for each replica r not in ISR if ( r.leo - leo_min < MIN_BYTES_LAG) newISR = ISR + r update the LeaderAndISR path in ZK with newISR the update is conditional and only succeeds if the version of the LeaderAndISR path in ZK is the same as leader.LeaderAndISRVersionInZK if (update in ZK successful) { leader.LeaderAndISRVersionInZK = new version of the LeaderAndISR path in ZK leader.ISR = new ISR } } At the follower: ReplicaFetcherThread for Replica r run() { while(true) { send ReplicaFetchRequest to leader and get response:ReplicaFetcherResponse back append response.messages to r's log r.hw = response.hw advance offset in ReplicaFetchRequest } } |
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