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https://issues.apache.org/jira/browse/HADOOP-6904?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12935211#action_12935211
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Sanjay Radia commented on HADOOP-6904:
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Hairong, to summarize our discussion today:
GetProtocolVersion() could return the server method names; we can optimize
this if the version numbers match exactly.
This would allow the client side to determine what is supported on SS without
having a messy switch statement on the V#.
The main issue you raised is how do we return this to the caller of getProxy().
The two options we discussed were
* when Proxy#getProtocolVersion() is called, the proxy can return the cached
info that it obtained when getProtocolVersion() was first called.
* let getProxy() return an object that contains the proxy object and also the
M#, m# and the method names/signatures.
> 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, 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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