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https://issues.apache.org/jira/browse/HADOOP-6729?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12861657#action_12861657
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Tom White commented on HADOOP-6729:
-----------------------------------
The JavaSerialization was written as an experimental serialization, to prove
the abstraction. I'm not sure it should be enabled by default since it's not
efficient, hasn't been tested at scale (as far as I know), and we should
encourage users to use other serializations like Writables or Avro.
In any case, we could improve the error message if the type is Serializable, or
print a warning.
> serializer.JavaSerialization should be added to io.serializations by default
> ----------------------------------------------------------------------------
>
> Key: HADOOP-6729
> URL: https://issues.apache.org/jira/browse/HADOOP-6729
> Project: Hadoop Common
> Issue Type: Improvement
> Components: conf
> Affects Versions: 0.20.2
> Reporter: Ted Yu
>
> org.apache.hadoop.io.serializer.JavaSerialization isn't included in
> io.serializations by default.
> When a class which implements the Serializable interface is used, user would
> see the following without serializer.JavaSerialization:
> java.lang.NullPointerException
> at
> org.apache.hadoop.io.serializer.SerializationFactory.getSerializer(SerializationFactory.java:73)
> at
> org.apache.hadoop.mapred.MapTask$MapOutputBuffer.<init>(MapTask.java:759)
> at
> org.apache.hadoop.mapred.MapTask$NewOutputCollector.<init>(MapTask.java:487)
> at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:575)
> at org.apache.hadoop.mapred.MapTask.run(MapTask.java:305)
> at org.apache.hadoop.mapred.Child.main(Child.java:170)
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