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Posted to common-issues@hadoop.apache.org by "Hairong Kuang (JIRA)" <ji...@apache.org> on 2011/01/04 23:31:50 UTC
[jira] Updated: (HADOOP-6904) A baby step towards inter-version
communications between dfs client and NameNode
[ https://issues.apache.org/jira/browse/HADOOP-6904?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Hairong Kuang updated HADOOP-6904:
----------------------------------
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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