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From "Hairong Kuang (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-6904) A baby step towards inter-version communications between dfs client and NameNode
Date Fri, 06 Aug 2010 21:55:18 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-6904?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Hairong Kuang updated HADOOP-6904:
----------------------------------

    Attachment: rpcVersion.patch

Here is a patch for review.

1. It introduces a new exception VersionIncompatible means that the server is not able to
serve the client because they are not compatible, while VersionMismatch only means that the
client and server have different versions and the server could not determine if the client
is compatible with the server or not.

2. It adds a set of unit tests to illustrate how client & server can talk across-versions.

Other changes are trivial.

> 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
>
>
> 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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