Table of Contents

Status

Current state: Under Discussion

...

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 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.

...

We need a throttling mechanism in the client-side to give administrators control over Kafka's impact on ZooKeeper, and for this we propose a new broker config called zookeeper.max.in.flight.requests.

Public Interfaces

This KIP only adds a new broker configuration described below.

Proposed Changes

This KIP proposes a new broker config called zookeeper.max.in.flight.requests which represents the maximum number of unacknowledged requests the client will send to ZooKeeper before blocking.

...

The default value is set to 10. We ran experiments showing the impact of zookeeper.max.in.flight.requests on completion times for various ZooKeeper-intensive controller protocols. The default was chosen to be the smallest number beyond which the experiment results have found diminishing returns.

Compatibility, Deprecation, and Migration Plan

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.

Rejected Alternatives

Several options for the default value were considered:

...