Status

Current state: [Under Discussion]

Discussion thread: here 

JIRA: here 

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

Motivation

window.size.ms  is not a true KafkaStreams config, and results in an error when set from a KStreams application. It belongs on the client.

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.

• docs/streams/developer-guide/config-streams

Proposed Changes

I propose we deprecate window.size.ms  in StreamsConfig.

Note: It might seem that `window.inner.serde` is similar, but if you refer to TimeWindowedSerializer  you will see that it is indeed used by KafkaStreams. 

Compatibility, Deprecation, and Migration Plan

• What impact (if any) will there be on existing users? Deprecating it in StreamsConfig  shouldn't impact current users negatively other than them seeing a warning when they use it in KStreams.  

• If we are changing behavior how will we phase out the older behavior? We should change the config docs first to deprecate. In the future, moving the configuration to ClientConfig could be called for. See https://github.com/apache/kafka/pull/14360 for a PR in progress, as well as a discussion of this issue.
• If we need special migration tools, describe them here. N/A
• When will we remove the existing behavior? Post docs change and deprecation, for major release 5. Deprecation itself can be for next minor release. 

Test Plan

Could be covered with a unit test to check that a warning is displayed when used.

Rejected Alternatives

Currently N/A.