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From "Tsz Wo (Nicholas), SZE (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1329) A baby step towards inter-version communications between dfs client and NameNode
Date Tue, 03 Aug 2010 15:09:18 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1329?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12894897#action_12894897

Tsz Wo (Nicholas), SZE commented on HDFS-1329:

Could you provide a few examples of compatible changes to ClientProtocol?  I wonder how could
a DfsClient check whether it is compatible to the server.  Are there rules?  or just by a
hard coded compatibility list?

The description is quite abstract.  I do not understand what are the goals.  Could you tell
us your use cases?

> A baby step towards inter-version communications between dfs client and NameNode
> --------------------------------------------------------------------------------
>                 Key: HDFS-1329
>                 URL: https://issues.apache.org/jira/browse/HDFS-1329
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>          Components: hdfs client
>    Affects Versions: 0.22.0
>            Reporter: Hairong Kuang
>            Assignee: Hairong Kuang
>             Fix For: 0.22.0
> 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
> 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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