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Date: Thu, 26 Jul 2012 22:57:34 +0000 (UTC)
From: "Brandon Li (JIRA)" <jira@apache.org>
To: common-issues@hadoop.apache.org
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Subject: [jira] [Commented] (HADOOP-8619) WritableComparator must implement
 no-arg constructor
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    [ https://issues.apache.org/jira/browse/HADOOP-8619?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13423527#comment-13423527 ] 

Brandon Li commented on HADOOP-8619:
------------------------------------

Thanks for finding the issue. The patch should fix the problem.

Actually in Hadoop core components, instead of java Serialization, interface "Writable" is wildly used to do in-memory(or on disk persistence) serialization and Protobuf is used for remote communication.
                
> WritableComparator must implement no-arg constructor
> ----------------------------------------------------
>
>                 Key: HADOOP-8619
>                 URL: https://issues.apache.org/jira/browse/HADOOP-8619
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: io
>    Affects Versions: 3.0.0
>            Reporter: Radim Kolar
>             Fix For: 0.23.0, 2.0.0-alpha, 3.0.0
>
>         Attachments: writable-comparator.txt
>
>
> Because of reasons listed here: http://findbugs.sourceforge.net/bugDescriptions.html#SE_COMPARATOR_SHOULD_BE_SERIALIZABLE
> comparators should be serializable. To make deserialization work, it is required that all superclasses have no-arg constructor. http://findbugs.sourceforge.net/bugDescriptions.html#SE_NO_SUITABLE_CONSTRUCTOR
> Simply add no=arg constructor to  WritableComparator.

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