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https://issues.apache.org/jira/browse/HADOOP-6904?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12965354#action_12965354
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Sanjay Radia commented on HADOOP-6904:
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@Dhruba
>major/minor numbers can be considered an optimization, isn't it?
The M-m# allows one to assert compatibility; the other way is via method name
comparison. I see them as complementary rather than
as an optimization. Without the major minor number one has to do a check on
each call or do a check on the getProxy. The real difference is the following:
if you check during getProx() and a method is missing then how does one assert
that it is still okay to connect because the missing method is actually a new
method and the call can return a non-implemented exception; with M-m# one can
assert this because when the M# has not changed and hence one is assured that
the method was not deleted and it must be a new method.
If you look at the example of list() call I gave above, the method names give
a minor simplification of the code.
I have no issues with passing the method names as long as we also optimize by
not sending the list when there is match of version numbers. I also believe we
will have to cache the results across reconnects (BTW we had discussed the same
optimization for
Avro RPC except that it uses the schema checksum).
> 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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