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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 Wed, 24 Nov 2010 20:03:16 GMT

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

Hairong Kuang updated HADOOP-6904:

    Attachment: majorMinorVersion1.patch

A new patch is attached. This is a little bit different from Sanjay's summary:
1. getProxy or waitProxy returns an object that contains the reference to the RPC proxy and
the server version #. The caller of getProxy/waitProxy could cache the server version# by
2. getProtocolVersion will always get the server version from the server side.

Returning methods that supported at the server side along with getProtocolVersion is a good
solution to support across branch client/server RPCs. Dhruba is especially interested in this
approach. Lets get back to this after we put more thoughts. For this jira, I prefer to go
with the version# for now.

> 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,
> 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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