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https://issues.apache.org/jira/browse/HADOOP-6904?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Hairong Kuang updated HADOOP-6904:
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Attachment: rpcCompatible-trunk.patch
Ok, I finally got some time to work on this. Here comes the first draft.
1. getProtocolVersion has a new signature:
a. it in addition sends the hashcode of client-side protocol methods;
b. it returns the server's version number and an array of hash codes of
server protocol's methods if the client protocol is different from the server
side protocol.
2. getProxy returns a new type ProtocolServer which contains
a. the proxy to communicate with server;
b. a method to check if a client side method is supported at the server side
or not.
3. A unit test TestRPCCompatibility to illustrate how to write compatible RPCs.
> 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,
> rpcCompatible-trunk.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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