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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-252) add versioning to RPC
Date Wed, 24 May 2006 22:52:30 GMT
    [ http://issues.apache.org/jira/browse/HADOOP-252?page=comments#action_12413191 ] 

Doug Cutting commented on HADOOP-252:
-------------------------------------

One complication is that different RPC protocols share common connections, in order to minimize
the number of per-connection threads and sockets.  So the versions would really need to be
transmitted with each request, or perhaps with the first request of each protocol over a given
connection.

> add versioning to RPC
> ---------------------
>
>          Key: HADOOP-252
>          URL: http://issues.apache.org/jira/browse/HADOOP-252
>      Project: Hadoop
>         Type: Improvement

>   Components: ipc
>     Reporter: Yoram Arnon

>
> currently, any change to any rpc message breaks the protocol, with mysterious exceptions
occurring at run time.
> a versioning sceme would have two benefits:
> - intelligent error messages, indicating that an upgrade is required
> - backwards compatibility could be supported.
> the proposal is to add a "const version" for each protocol, and a method: int getVersion(int
version) that sends the client's version and receives the server's version. This would be
the first method invoked on connection. Both sides then either agree on the lowest version
number, providing backwards compatibility support, or abort the connection as "unsupported
version".

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