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https://issues.apache.org/jira/browse/HADOOP-7328?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13050626#comment-13050626
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Harsh J commented on HADOOP-7328:
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I actually do have two comments of concern w.r.t. front-end & throwing:
If we are to make code changes _throw-y_, then it would require that all places
that use the said API inside Hadoop add throws IOException to their methods.
Upon a quick check, only one single SequenceFile private utility method
required this change, and none in MapReduce. But it could've been that the
change required subsequent public API changes.
Since we've never had front end checks for MR serializers before; if people
relied on passing strings over to job.xml and have it resolve only on worker
machines - the related issue may break this functionality. Guideline-wise, its
a wrong way to do it, but I think it still breaks something deep below I think.
But I think its worth enforcing this check (null handling later or throw above,
either way) since it makes stuff like job setup errors quicker to debug and
iterate upon.
> Give more information about a missing Serializer class
> ------------------------------------------------------
>
> Key: HADOOP-7328
> URL: https://issues.apache.org/jira/browse/HADOOP-7328
> Project: Hadoop Common
> Issue Type: Improvement
> Components: io
> Affects Versions: 0.20.2
> Reporter: Harsh J
> Assignee: Harsh J
> Labels: io, serialization
> Fix For: 0.23.0
>
> Attachments: HADOOP-7328.r1.diff, HADOOP-7328.r2.diff,
> HADOOP-7328.r3.diff
>
>
> When you have a key/value class that's non Writable and you forget to attach
> io.serializers for the same, an NPE is thrown by the tasks with no
> information on why or what's missing and what led to it. I think a better
> exception can be thrown by SerializationFactory instead of an NPE when a
> class is not found accepted by any of the loaded ones.
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