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Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

Motivation

Jira
server ASF JIRA serverId 5aa69414-a9e9-3523-82ec-879b028fb15b key KAFKA-5501

introduced  introduced a ZooKeeper client wrapper called kafka.zookeeper.ZooKeeperClient that encourages pipelined requests to zookeeper. This client pipelines requests to ZooKeeper by performing a "scatter-gather" of asynchronous calls provided by the underlying org.apache.zookeeper.ZooKeeper client. That is, the client would send a pipelined sequence of requests and wait for all of their responses.

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From a protocol standpoint, the change is fully backwards compatible. Setting the default value to 10 implies administrators may see an increase in load in ZooKeeper than what was seen prior to the controller using kafka.zookeeper.ZooKeeperClient in

Jira
server ASF JIRA serverId 5aa69414-a9e9-3523-82ec-879b028fb15b key KAFKA-5642

. Those who wish to retain existing ZooKeeper load should set zookeeper.max.in.flight.requests to 1.

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