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Status

Current state: Draft

Discussion thread: here [Change the link from the KIP proposal email archive to your own email thread]

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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

Proposed Changes

Since Scala 2 is not binary compatible across minor versions, a separate kafka  (aka core ) artifact is published for each supported Scala version (as is typical for Scala projects). More concretely, we currently publish kafka_2.12 and kafka_2.13 for Scala 2.12 and 2.13 respectively. This requires building the project and running all the tests once for each supported Scala version. In addition, it's not uncommon for contributors to have to fix pull requests so that they work on both Scala versions).

Projects written in Java can use any of the two jars (i.e. there is no benefit in having both artifacts), but projects written in Scala should use the jar with the matching Scala version. It is worth noting that the kafka  jar does not expose any public API, so we are doing extra work to support Scala users who access internal APIs. That said, it's not uncommon for users and other projects to depend on internal broker classes to start an embedded kafka cluster for testing purposes (we should have a public API for testing, but that's a subject for another KIP).

As part of KIP-751, we deprecated support for Scala 2.12 with the goal to remove it in Apache 4.0 – that is, a single Scala version would be supported at that point. I propose we take the chance to formalize that only a single Scala version will be supported at any point in time from Apache Kafka 4.0 and the artifact name should be changed to be simply kafka  (i.e. the Scala version suffix would be removed).

Public Interfaces

Rename kafka_2.13  to kafka  in Apache Kafka 4.0.

Proposed Changes

Update the build to achieve what's been mentioned in the Public Interfaces  sectionDescribe 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.

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?

Test Plan

Describe in few sentences how the KIP will be tested. We are mostly interested in system tests (since unit-tests are specific to implementation details). How will we know that the implementation works as expected? How will we know nothing broke?

Rejected Alternatives

Users and projects that depend on kafka_2.13  would have to change their build to refer to kafka .

Projects written in Scala that are using a different version than the one kafka  supports would have to either use a separate classloader, shading or running kafka in a separate process via testcontainers (or similar).

Test Plan

Verify that the published artifact has the updated name.

Rejected Alternatives

Maintain the status quoIf 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.