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https://issues.apache.org/jira/browse/HBASE-9681?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13788357#comment-13788357
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Andrew Purtell commented on HBASE-9681:
---------------------------------------

bq, Small clarification - why does there have to be an invalid message? If it's 
a separate method/message, when the new client attempts to send it to an old 
server, it will get an easily recognizable exception back, right?

For the old server it's an invalid message. Ok, there I agree that's over 
specified, I had one thing in mind but it's not the only way.

> Basic codec negotiation
> -----------------------
>
>                 Key: HBASE-9681
>                 URL: https://issues.apache.org/jira/browse/HBASE-9681
>             Project: HBase
>          Issue Type: Sub-task
>    Affects Versions: 0.98.0
>            Reporter: Andrew Purtell
>
> Basic codec negotiation:
> There should be a default codec used for cell encoding over the RPC 
> connection. This should be configurable in the site file. 
> The client can optionally send a message, a manufactured "call" that would 
> otherwise be invalid in some way, to the server asking for a list of 
> supported cell codecs. An older server should simply send back an error 
> because the request is invalid except to servers supporting this feature. A 
> server supporting this feature should send back the requested information or 
> an error indication if something went wrong.
> The client can optionally send a message, a manufactured "call" that would 
> otherwise be invalid in some way, to the server asking for it to use a given 
> codec for all further communication. Otherwise the server will continue to 
> use the default codec. The server will send back a call response 
> acknowledging the change or an error indication if the request cannot be 
> honored.
> Server configuration should support mappings from one codec type to another. 
> We need to handle the case where the server has a codec available that 
> extends the requested type but overrides some behavior in the base class, and 
> this is what should be used in lieu of the base type. It must also be 
> possible to choose an alternate default codec which stands in for the default 
> codec, is compatible with client expectations, but changes the server side 
> behavior as needed in the absence of negotiation. 



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