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From David Arthur <mum...@gmail.com>
Subject Re: versionId in responses (and general API versioning questions)
Date Tue, 19 Feb 2013 18:34:02 GMT
I have created https://issues.apache.org/jira/browse/KAFKA-759 to remove 
versionId as discussed

On 2/13/13 7:40 PM, David Arthur wrote:
> On 2/13/13 4:08 PM, Jay Kreps wrote:
>> Hey David,
>> We ended up not versioning the response, instead the version must
>> correspond to the request version.
>> This makes sense from the client point of view. If you send a request
>> using version X of the protocol you know you will get a response in
>> format X. Separately versioning the response would seem to indicate
>> that the server is allowed to send back a different version of the
>> response. This means the client has to check this and handle old
>> response versions (and what would it even do with newer versions?).
> This makes complete sense. I was confused since OffsetCommit/Fetch are 
> including it in the responses
>> Instead we thought it makes more sense to make the server deal with
>> compatibility only. So the versioning is at the request/response pair
>> and the server is required to always send the correct version of the
>> response for all supported request versions.
>> I just noticed that your responses for the offset apis actually have a
>> version. We should probably remove that before the release.
> Yea, agreed.
>> -Jay
>> On Wed, Feb 13, 2013 at 12:48 PM, David Arthur <mumrah@gmail.com> wrote:
>>> Just noticed that most of the API response structs do not include the
>>> ApiVersion. This will make it hard for clients to determine how to 
>>> handle
>>> responses once the APIs start getting updated (which is pretty much
>>> inevitable).
>>> I'd propose we update the standard response envelope to include it
>>> Response => ApiVersion CorrelationId ResponseMessage
>>>    ApiVersion => int16
>>>    CorrelationId => int32
>>>    ResponseMessage => ...
>>> Otherwise, it seems we must freeze the response formats forever.
>>> Another thought is that the server should return the same version of 
>>> the API
>>> that was requested (if a client sends in v1, then presumably it does 
>>> know
>>> about any future versions...). How will this work? This seems to imply
>>> backwards compat for the APIs like Avro.
>>> Thoughts?
>>> -David

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