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https://issues.apache.org/jira/browse/HADOOP-6904?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12979871#action_12979871
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Hairong Kuang commented on HADOOP-6904:
---------------------------------------
> If the client must provide an interface name that the server then uses to
> identify the set of methods to fingerprint.
Client must provide an interface name but the server may choose not to
verify/choose it. This decision simply makes the server implementation more
flexible. getProtocolSignature is called only once when the client connects to
the server. I do not think we should scarifies flexibility for performance.
Look at the unit test TestRPCCompatibility#TestImpl0 that I provide. It does
not use the client provided protocol name.
{code}
@Override
public ProtocolSignature getProtocolSigature(String protocol,
long clientVersion, int clientMethodsHashCode)
throws IOException {
Class<? extends VersionedProtocol> inter;
try {
inter = (Class<? extends
VersionedProtocol>)getClass().getGenericInterfaces()[0];
} catch (Exception e) {
throw new IOException(e);
}
return ProtocolSignature.getProtocolSignature(clientMethodsHashCode,
getVersion(), inter);
}
{code}
> 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, 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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