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We will stop accepting request.required.acks > 1 from clients implementing the new version of the protocol and may return a new error code.

Proposed Change

ProducerRequest protocol version will be bumped to 1.

We will add a new error to the client protocol: InvalidRequiredAcksException (error_code = 21)

In version 0.8.2, when Kafka broker receives request with acks > 1, we will log a warning to server log. The warning will include client_id, client IP and the number of acks. This will allow cluster admins to bring clients into compliance before we remove support of this configuration.

In version 0.8.3 requestIf ProduceRequest version = 1, we will check request.required.acks of the request and return InvalidRequiredAcksException if request.required.acks > 1 If ProduceRequest version = 0, we will maintain current behavior, and log a WARN message in the broker about use of deprecated number of ackswill lead to error_code 21 sent to the client and an error logged to server log.

Migration Plan, Compatibility and Deprecation

Users upgrading to clients that implement new version of protocol brokers to 0.8.3 will need to change their configuration and avoid request.required.acks >1. We will support existing behavior and version 0 of the protocol for

0.8.X versions. I suggest deprecating for 0.9.3 Java clients will get a InvalidRequiredAcksException. Other clients will get error code 21. 

Rejected Alternatives

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1. Silently replace request.required.acks>1 with request.required.acks=-1. Rejected as possibly very confusing to users who will see higher latency (and possibly lower reliability) with no explanation.

Questions that may need more debate

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1. Bump protocol version to 1 to indicate new behavior and new error code, and support both behaviors in 0.8.3. Rejected as an overkill.