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Status

Current state: "Under Discussion"

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

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

The metadata version (MV) is used to define the on disk and over the wire record format for messages stored in the metadata log. A new metadata version is introduced each time a record format is changed or a new record is introduced to support a new feature. Examples of this are the support of SCRAM in MV IBP_3_5_IV2, support of Delegation Tokens in MV IBP_3_6_IV2 and the support of JBOD in MV IBP_3_7_IV2. All brokers and controllers must support a given MV before the cluster can start using that MV. 

The development of a feature that requires a new MV often requires multiple commits before the feature is complete, sufficiently tested and ready for production. Sometimes there is a need for multiple features to be developed at the same time and in some cases not all of these features with be complete and ready for production for a given release. In these scenarios we need to reorder MetadataVersions such that production ready features have their MV before those that are not ready.

Proposed Changes

The idea is to define a production-ready MetadataVersion defined in MetadataVersion.java as LATEST_PRODUCTION such that all MetadataVersions less than or equal to this value are stable and ready for production. Any MetadataVersion greater than this value is unstable and requires a special property to use in a cluster. Any unstable feature which requires a new MV can have that MV change, as other features with a higher MV become stable and ready for production.

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

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

If 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.