[jira] [Commented] (KAFKA-5642) Use async ZookeeperClient in Controller

["Ismael Juma (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-5642?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16101713#comment-16101713 ] 

Ismael Juma commented on KAFKA-5642:
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[~onurkaraman], I took a stab at splitting this JIRA into multiple ones. I think it will be easier to review if we do it this way instead of a single PR. If you have other ideas on how we should do it, happy to update things.

> Use async ZookeeperClient in Controller
> ---------------------------------------
>
>                 Key: KAFKA-5642
>                 URL: https://issues.apache.org/jira/browse/KAFKA-5642
>             Project: Kafka
>          Issue Type: Sub-task
>            Reporter: Onur Karaman
>            Assignee: Onur Karaman
>
> Synchronous zookeeper writes means that we wait an entire round trip before doing the next write. These synchronous writes are happening at a per-partition granularity in several places, so partition-heavy clusters suffer from the controller doing many sequential round trips to zookeeper.
> * PartitionStateMachine.electLeaderForPartition updates leaderAndIsr in zookeeper on transition to OnlinePartition. This gets triggered per-partition sequentially with synchronous writes during controlled shutdown of the shutting down broker's replicas for which it is the leader.
> * ReplicaStateMachine updates leaderAndIsr in zookeeper on transition to OfflineReplica when calling KafkaController.removeReplicaFromIsr. This gets triggered per-partition sequentially with synchronous writes for failed or controlled shutdown brokers.
> KAFKA-5501 introduced an async ZookeeperClient that encourages pipelined requests to zookeeper. We should replace ZkClient's usage with this client.



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