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https://issues.apache.org/jira/browse/HADOOP-7347?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13100456#comment-13100456
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Doug Cutting commented on HADOOP-7347:
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Adapters are a powerful concept, but difficult to maintain. I wonder how soon
we require them.
Adapters would be required to support interoperability between the
pre-evolvable parameter world and the evolvable parameter world since parameter
serialization will change fundamentally in that transition. But we only expect
to make that transition just once, so we perhaps needn't build a general
mechanism capable of handling such transitions?
Once we transition I think we'll be able to handle interoperability between
adjacent major versions using your rules 1-3. Prior to the transition we would
not provide wire compatibility between major versions. Do we expect protocol
changes that we cannot handle with rules 1-3?
Perhaps it comes down to whether we're willing to have another
non-interoperable major release. These are unfortunate, but a
non-interoperable release is not a regression, so I don't see it as a hard
requirement that we don't have another before we add interoperability as a
feature.
If interoperability is a requirement for future releases, then perhaps we
should push HDFS-2060 into 0.23. If we did that and in some subsequent release
decide we wish to incompatibly alter wire formats in some way that cannot be
handled with rules 1-3 then we could implement adapters. But we might have a
few interoperable releases in the meantime.
> HDFS Wire compatibility
> -----------------------
>
> Key: HADOOP-7347
> URL: https://issues.apache.org/jira/browse/HADOOP-7347
> Project: Hadoop Common
> Issue Type: Improvement
> Reporter: Sanjay Radia
> Assignee: Sanjay Radia
> Fix For: 0.23.0
>
> Attachments: Wire Compatibility – Separating wire types.pdf
>
>
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