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https://issues.apache.org/jira/browse/HADOOP-7021?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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John Lee updated HADOOP-7021:
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Attachment: HADOOP-7021.patch
> MapWritable NullPointerException
> --------------------------------
>
> Key: HADOOP-7021
> URL: https://issues.apache.org/jira/browse/HADOOP-7021
> Project: Hadoop Common
> Issue Type: Bug
> Components: io
> Affects Versions: 0.20.1, 0.21.0
> Environment: Hadoop 0.20.1, Centos
> Reporter: John Lee
> Priority: Minor
> Fix For: 0.20.1
>
> Attachments: HADOOP-7021.patch, HADOOP-7021.patch
>
>
> We have encountered a NullPointerException when we use MapWritable with
> custom Writable objects.
> The root cause is the counter newClasses in AbstractMapWritable is allowed to
> get out of sync with the id to class mapping tables when addToMap(Class) is
> called. We have a patch to AbstractMapWritable.addToMap(Class) that handles
> the case when newClasses gets out of sync with the id to class mapping tables
> and adds a serialization optimization to minimize the number of class names
> to write out per MapWritable object.
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