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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-7347) HDFS Wire compatibility
Date Thu, 08 Sep 2011 17:06:08 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-7347?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13100456#comment-13100456

Doug Cutting commented on HADOOP-7347:

Adapters are a powerful concept, but difficult to maintain.  I wonder how soon we require

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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