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From "Andrew Wang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-6984) In Hadoop 3, make FileStatus serialize itself via protobuf
Date Fri, 09 Dec 2016 20:23:58 GMT

    [ https://issues.apache.org/jira/browse/HDFS-6984?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15736258#comment-15736258
] 

Andrew Wang commented on HDFS-6984:
-----------------------------------

Here's also a more radical idea: how about we simply stop implementing Writable altogether
in FileStatus? I did an empirical test by successfully building all of CDH with a patch that
does this. This includes apps like HBase, Hive, Spark, Solr, Impala, Oozie, Avro, Parquet,
etc.

I'm guessing FileStatus was originally made Writable as a shortcut for DistCp. Maybe there
are custom apps that use Writable, but the vast majority of Cloudera users interact with a
Hadoop cluster via a higher-level framework.

> In Hadoop 3, make FileStatus serialize itself via protobuf
> ----------------------------------------------------------
>
>                 Key: HDFS-6984
>                 URL: https://issues.apache.org/jira/browse/HDFS-6984
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>    Affects Versions: 3.0.0-alpha1
>            Reporter: Colin P. McCabe
>            Assignee: Colin P. McCabe
>              Labels: BB2015-05-TBR
>         Attachments: HDFS-6984.001.patch, HDFS-6984.002.patch, HDFS-6984.003.patch, HDFS-6984.nowritable.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 serialize itself via protobuf 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 existing FileStatus serialization there.



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