Thank you for the clear proposal, Grant! I like the request/response objects and the timeout semantics. Two comments:
1. The replica assignment protocol takes [replicas], there is the implicit assumption that the first replica is the leader. This matches current behavior elsewhere, but lets document it explicitly. 2. I like the timeout, but want to clarify why, since it may not be obvious to everyone: Currently, the response is sent when the controller has sent the "update metadata" request to the brokers involved with the new topic. It is a rather weak guarantee, but if clients decide to poll the brokers for updates, it does reduce the time spent polling. More important, this behavior is net improvement on current state (completely async and ZK dependent) and when we do have a way to get "ack" from replicas, we will be able to add the new behavior without changing the protocol (just the semantics of waiting). Gwen On Fri, Jun 10, 2016 at 7:21 PM, Grant Henke <ghe...@cloudera.com> wrote: > Now that Kafka 0.10 has been released I would like to start work on the new > protocol messages and client implementation for KIP-4. In order to break up > the discussion and feedback I would like to continue breaking up the > content in to smaller pieces. > > This discussion thread is for the CreateTopic request/response and server > side implementation. Details for this implementation can be read here: > https://cwiki.apache.org/confluence/display/KAFKA/KIP-4+-+Command+line+and+centralized+administrative+operations#KIP-4-Commandlineandcentralizedadministrativeoperations-CreateTopicRequest > > I have included the exact content below for clarity: > >> Create Topic Request (KAFKA-2945 >> <https://issues.apache.org/jira/browse/KAFKA-2945>) >> >> >> CreateTopic Request (Version: 0) => [create_topic_requests] timeout >> create_topic_requests => topic partitions replication_factor >> [replica_assignment] [configs] >> topic => STRING >> partitions => INT32 >> replication_factor => INT32 >> replica_assignment => partition_id [replicas] >> partition_id => INT32 >> replicas => INT32 >> configs => config_key config_value >> config_key => STRING >> config_value => STRING >> timeout => INT32 >> >> CreateTopicRequest is a batch request to initiate topic creation with >> either predefined or automatic replica assignment and optionally topic >> configuration. >> >> Request semantics: >> >> 1. Must be sent to the controller broker >> 2. Multiple instructions for the same topic in one request will be >> silently ignored, only the last from the list will be executed. >> - This is because the list of topics is modeled server side as a >> map with TopicName as the key >> 3. The principle must be authorized to the "Create" Operation on the >> "Cluster" resource to create topics. >> - Unauthorized requests will receive a ClusterAuthorizationException >> 4. >> >> Only one from ReplicaAssignment or (Partitions + ReplicationFactor), can >> be defined in one instruction. If both parameters are specified - >> ReplicaAssignment takes precedence. >> - In the case ReplicaAssignment is defined number of partitions and >> replicas will be calculated from the supplied ReplicaAssignment. >> - In the case of defined (Partitions + ReplicationFactor) replica >> assignment will be automatically generated by the server. >> - One or the other must be defined. The existing broker side auto >> create defaults will not be used >> (default.replication.factor, num.partitions). The client >> implementation can >> have defaults for these options when generating the messages. >> 5. Setting a timeout > 0 will allow the request to block until the >> topic metadata is "complete" on the controller node. >> - Complete means the topic metadata has been completely populated >> (leaders, replicas, ISRs) >> - If a timeout error occurs, the topic could still be created >> successfully at a later time. Its up to the client to query for the >> state >> at that point. >> 6. The request is not transactional. >> 1. If an error occurs on one topic, the other could still be >> created. >> 2. Errors are reported independently. >> >> QA: >> >> - Why is CreateTopicRequest a batch request? >> - Scenarios where tools or admins want to create many topics should >> be able to with fewer requests >> - Example: MirrorMaker may want to create the topics downstream >> - What happens if some topics error immediately? Will it >> return immediately? >> - The request will block until all topics have either been created, >> errors, or the timeout has been hit >> - There is no "short circuiting" where 1 error stops the other >> topics from being created >> - Why implement "partial blocking" instead of fully async of fully >> consistent? >> - See Cluster Consistent Blocking >> >> <https://cwiki.apache.org/#KIP-4-Commandlineandcentralizedadministrativeoperations-clusterconsistentblocking> >> below >> - Why require the request to go to the controller? >> - The controller is responsible for the cluster metadata and >> its propagation >> - See Request Forwarding >> >> <https://cwiki.apache.org/#KIP-4-Commandlineandcentralizedadministrativeoperations-request> >> below >> >> Create Topic Response >> >> >> CreateTopic Response (Version: 0) => [topic_error_codes] >> topic_error_codes => topic error_code >> topic => STRING >> error_code => INT16 >> >> CreateTopicResponse contains a map between topic and topic creation >> result error code (see New Protocol Errors >> <https://cwiki.apache.org/confluence/display/KAFKA/KIP-4+-+Command+line+and+centralized+administrative+operations#KIP-4-Commandlineandcentralizedadministrativeoperations-NewProtocolErrors> >> ). >> > > A sample PR is on github (https://github.com/apache/kafka/pull/1489) though > it could change drastically based on the feedback here. > > Thanks, > Grant > > -- > Grant Henke > Software Engineer | Cloudera > gr...@cloudera.com | twitter.com/gchenke | linkedin.com/in/granthenke
