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https://issues.apache.org/jira/browse/HADOOP-6904?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12980275#action_12980275
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Doug Cutting commented on HADOOP-6904:
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This is looking good!
The cache might better be a Map<Class,ProtocolSignature>. Then you could avoid
calling Class#getMethods(), 'new ProtocolSignature()', etc. for most calls to
ProtocolSignature.getProtocolSignature(). You might add a
ProtocolSignature(Class) constructor, and change the other constructor to
either ProtocolSignature(int, int[]) or perhaps just ProtocolSignature(int),
since null is always passed as the second parameter.
Also, a very minor nit, do you need to call Integer.valueOf() and/or
intValue()? Wouldn't autoboxing do the right thing there?
> A baby step towards inter-version RPC communications
> ----------------------------------------------------
>
> 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: 0.23.0
>
> Attachments: majorMinorVersion.patch, majorMinorVersion1.patch,
> rpcCompatible-trunk.patch, rpcCompatible-trunk1.patch,
> rpcCompatible-trunk2.patch, rpcCompatible-trunk4.patch,
> rpcCompatible-trunk5.patch, rpcCompatible-trunk6.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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