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From "Hairong Kuang (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-6904) A baby step towards inter-version RPC communications
Date Thu, 27 Jan 2011 20:11:46 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-6904?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Hairong Kuang updated HADOOP-6904:
----------------------------------

    Attachment: rpcCompatible-trunk10.patch

RpcCompatible-trunk10.patch has a few more changes. Most of then are done either to allow
less code change to the rest of Hadoop code or make less disruptive to the current Hadoop
depoyment.
1. VersionedProtocol keeps the old API: getProtocolVersion for backwards compatibility purpose.
I just found out that HBase RPC uses VersionedProtocol too. So keeping the old API would allow
the old Hadoop RPC client to continue to talk to the new RPC server.
2. Change PROTOCOL_FINGERPRINT_CACHE to be HashMap and instead make getSigFingerprint to be
synchronized on the hashmap.
3. Add a new static method in ProtocolSignature which all RPC servers could use:
{code}
  public static ProtocolSignature getProtocolSigature(VersionedProtocol server,
      String protocol,
      long clientVersion, int clientMethodsHash) throws IOException;
{code}
4. keep the old getProxy/waitProxy APIs to allow less code change to the rest of the Hadoop
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-trunk10.patch, rpcCompatible-trunk2.patch, rpcCompatible-trunk4.patch,
rpcCompatible-trunk5.patch, rpcCompatible-trunk6.patch, rpcCompatible-trunk7.patch, rpcCompatible-trunk8.patch,
rpcCompatible-trunk9.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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