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From "Chris Nauroth (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-6984) In Hadoop 3, make FileStatus no longer a Writable
Date Fri, 05 Sep 2014 19:11:31 GMT

    [ https://issues.apache.org/jira/browse/HDFS-6984?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14123412#comment-14123412
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Chris Nauroth commented on HDFS-6984:
-------------------------------------

bq. So, it looks like DistCp depends on FileStatus being writable...

Last time I looked at this, I actually planned on replacing DistCp's usage of {{FileStatus}}
serialization with its own custom data type.  I believe it doesn't need all of the fields
of {{FileStatus}}, so there is potential for a marginal space/performance improvement by omitting
the unnecessaries.

> In Hadoop 3, make FileStatus no longer a Writable
> -------------------------------------------------
>
>                 Key: HDFS-6984
>                 URL: https://issues.apache.org/jira/browse/HDFS-6984
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>    Affects Versions: 3.0.0
>            Reporter: Colin Patrick McCabe
>            Assignee: Colin Patrick McCabe
>         Attachments: HDFS-6984.001.patch
>
>
> FileStatus was a Writable in Hadoop 2 and earlier.  Originally, we used this to serialize
it and send it over the wire.  But in Hadoop 2 and later, we have the protobuf {{HdfsFileStatusProto}}
which serves to serialize this information.  The protobuf form is preferable, since it allows
us to add new fields in a backwards-compatible way.  Another issue is that already a lot of
subclasses of FileStatus don't override the Writable methods of the superclass, breaking the
interface contract that read(status.write) should be equal to the original status.
> In Hadoop 3, we should just make FileStatus no longer a writable so that we don't have
to deal with these issues.  It's probably too late to do this in Hadoop 2, since user code
may be relying on the ability to use the Writable methods on FileStatus objects there.



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