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Message-ID: <13848778.51701291229293752.JavaMail.jira@thor>
Date: Wed, 1 Dec 2010 13:48:13 -0500 (EST)
From: "Hairong Kuang (JIRA)" <jira@apache.org>
To: common-issues@hadoop.apache.org
Subject: [jira] Commented: (HADOOP-6904) A baby step towards inter-version
 communications between dfs client and NameNode
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    [ https://issues.apache.org/jira/browse/HADOOP-6904?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12965791#action_12965791 ] 

Hairong Kuang commented on HADOOP-6904:
---------------------------------------

GetProtocolVersion will be sure to send major version number. This is for judging if client/server are compatible or not.

We could either send minor version or a list of method names. From a programmer's point of view, using method names seems less error-prone.

> 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: majorMinorVersion.patch, majorMinorVersion1.patch, 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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