THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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- Listeners Registered to Zookeeper.
- AddPartitionsListener
- BrokerChangeListener
- DeleteTopicListener
- PartitionReassignedListener(Admin)
- PreferredReplicaElectionListener(Admin)
- ReassignedPartitionsIsrChangeListener
- TopicChangeListener
- Channels to brokers (controlled shutdown)
- Internal scheduled tasks (preferred leader election)
State change
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execution:
- Listener threads, KafkaApi thread and internal scheduler thread makes state change concurrently.
State change propagation model:
- P2P blocking channel from controller to each broker.
- Dedicated message queue for each controller-to-broker connection.
- No synchronization on message sent to different brokers.
- No callback for sending messages except topic deletion.
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- State change are executed by different listeners concurrently. Hence complicated synchronization is needed which is error prone and difficult to debug.
- State propagation is not synchronized. Brokers might be in different state for undetermined time. This leads to unnecessary extra data loss.
- During controlled shutdown process, two connections are used for controller to broker communication. This makes state change propagation and controlled shutdown approval out of order.
New controller design
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Outline
We will keep maintained state and fail over/back model unchanged.
We are going to change the state change propagation model, state change execution and output of the state change input source. More specifically:
- Abstract the output of each state change input source to an event.
- Have a single execution thread to serially process events one at a time.
- The zk listeners are responsible for only context updating but not event execution.
- Use o.a.k.clients.NetworClient + callback for state change propagation.
We would also like to modify KafkaServer to use new NetworkClient and prioritize the controller-to-broker traffic.
Related tickets
KAFKA-2139, KAFKA-2029, KAFKA-1305 (and definitely some other tickets... Appreciate it if people can add it here.)
Architecture
- The Controller Context contains two kinds of information: cluster reachability and Topic State(Partition, Replica, Leaders, etc)
- Two types of ZK listeners:
- Responsible of updating cluster reachability by listening to broker path in zookeeper.
- Responsible for create events and add them to Event Queue.
- A controlled shutdown event will be generated when receive controlled shutdown from broker.
- The controlled shutdown process will be changed to make state change and controlled shutdown approval occur in order. (This might involve broker side change as well)
- Scheduled tasks (e.g. preferred leader election) will
- Event Executor Thread:
- Change Topic State in Controller Context
- Propagate the new state to each broker using o.a.k.clients.NetworkClient in non-blocking way.
- Broker will only trigger Zookeeper data change when:
- Broker is down (or long GC)
- New topic automatically created