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https://issues.apache.org/jira/browse/HADOOP-6904?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12969155#action_12969155
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Sanjay Radia commented on HADOOP-6904:
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The client side does not know what is *newly* added or deleted. All it has is
client and server side list of methods. The client also knows that the
major number has not changed (ie getProxy succeeded)-- ie the calls that work
should be called.
* For the optimized methods, an upper layer (say Hdfs or DfsClient) will check
to see if optimal method is available and if not it will call the non-optimized
method;
for this one has to consult the list of server methods. This matches the case
with the previous M-m# approach where one compared the minor number to see if
it supports the optimized method (see my list example above).
* For the rest of the methods , simply make the call; consulting the list of
server methods is an optimization for the failure case. Recall that for the
previous M-m# approach
we did NOT compare the m# but simply make the call.
(Dhruba, did you buy the use of the Major number along with method names?)
> 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,
> 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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