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https://issues.apache.org/jira/browse/HADOOP-6904?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12898410#action_12898410
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Hairong Kuang commented on HADOOP-6904:
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As a practice, I rewrote HDFS-946, improve listStatus performance, in a
backward compatibility way. So the idea is that if the NN is an old server, the
client sends the old RPC getListing or getFileInfo, which send back FileStatus
in full path name. If NN is a new server, the client send the new RPCs,
getHdfsLising or getHdfsFileInfo, which send back HdfsFileStatus that carries
only a local name in byte format.
Potentially HDFS-202 could also written in an backward compatible way. If new
server, client sends a request getting FileStatus with locations back together;
Otherwise, client first get FileStatus then sends separate RPC for block
location.
> 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: 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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