[jira] Commented: (HADOOP-6904) A baby step towards inter-version communications between dfs client and NameNode

["Sanjay Radia (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-6904?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12928287#action_12928287 ] 

Sanjay Radia commented on HADOOP-6904:
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> Would we be able to use the major and minor version number to automate this. 
hairong, you had mentioned that unfortunately doing this will not backwards compatible. 
How about adding a new method called getMajorMinorVersion()
If that method fails you fall back to the getProtocolVersion()
This means going forward we have a slightly simpler model for dealing with compatibility.
(Of course when Avro is inserted then we are not likely to need the version numbers at all.)

> A baby step towards inter-version communications between dfs client and NameNode
> --------------------------------------------------------------------------------
>
>                 Key: HADOOP-6904
>                 URL: https://issues.apache.org/jira/browse/HADOOP-6904
>             Project: Hadoop Common
>          Issue Type: New Feature
>          Components: ipc
>    Affects Versions: 0.22.0
>            Reporter: Hairong Kuang
>            Assignee: Hairong Kuang
>             Fix For: 0.22.0
>
>         Attachments: rpcVersion.patch, rpcVersion1.patch
>
>
> Currently RPC communications in Hadoop is very strict. If a client has a different version from that of the server, a VersionMismatched exception is thrown and the client can not connect to the server. This force us to update both client and server all at once if a RPC protocol is changed. But sometime different versions do not mean the client & server are not compatible. It would be nice if we could relax this restriction and allows us to support inter-version communications.
> My idea is that DfsClient catches VersionMismatched exception when it connects to NameNode. It then checks if the client & the server is compatible. If yes, it sets the NameNode version in the dfs client and allows the client to continue talking to NameNode. Otherwise, rethrow the VersionMismatch exception.

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