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Status

Current state: Under Discussion

Discussion thread: TBD

JIRA:here [Change the link from KAFKA-1 to your own ticket]

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

Motivation

Describe the problems you are trying to solve.

Public Interfaces

Briefly list any new interfaces that will be introduced as part of this proposal or any existing interfaces that will be removed or changed. The purpose of this section is to concisely call out the public contract that will come along with this feature.

A public interface is any change to the following:

• Binary log format

• The network protocol and api behavior

• Any class in the public packages under clientsConfiguration, especially client configuration

  • org/apache/kafka/common/serialization

  • org/apache/kafka/common

  • org/apache/kafka/common/errors

  • org/apache/kafka/clients/producer

  • org/apache/kafka/clients/consumer (eventually, once stable)

• Monitoring

• Command line tools and arguments

• Anything else that will likely break existing users in some way when they upgrade

As we are rolling out static membership for general Kafka client applications, we need to have persistent `group.instance.id` throughout restarts. One of the edge case is that we are currently using shared static integer field for thread-id incrementation for multiple stream instances on one single JVM. So it is very easily to fall into this example scenario with two stream instance A, B:

Instance A init one stream thread → Instance A init one stream thread → Instance B init one stream thread → Instance B init one stream thread

So instance ids being generated when two instances starts are : A-1, A-2, B-3, B-4

During one bounce, the order of initialization could change to:

Instance A init one stream thread → Instance B init one stream thread → Instance A init one stream thread → Instance B init one stream thread

And then change instance ids to : A-1, A-3, B-2, B-4

This means we are creating 4 new instance ids compared with previous round, so broker could no longer leverage the static information it stored. Basically, the scenario invalidates static membership effectiveness.

Proposed Changes

Describe the new thing you want to do in appropriate detail. This may be fairly extensive and have large subsections of its own. Or it may be a few sentences. Use judgement based on the scope of the change.

Public Interfaces

Compatibility, Deprecation, and Migration Plan

• What impact (if any) will there be on existing users?
• If we are changing behavior how will we phase out the older behavior?
• If we need special migration tools, describe them here.
• When will we remove the existing behavior?

Rejected Alternatives

• There is no anticipated broken  

Rejected Alternatives

N/AIf there are alternative ways of accomplishing the same thing, what were they? The purpose of this section is to motivate why the design is the way it is and not some other way.