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https://issues.apache.org/jira/browse/HADOOP-9295?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13582124#comment-13582124
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David Parks commented on HADOOP-9295:
-------------------------------------
I'd be happy to submit this as a patch, however I don't know what that entails,
can you point me to some documentation of the format you want it in, or offer
some help in doing that?
Thanks,
Dave
> AbstractMapWritable throws exception when calling readFields() multiple times
> when the maps contain different class types
> -------------------------------------------------------------------------------------------------------------------------
>
> Key: HADOOP-9295
> URL: https://issues.apache.org/jira/browse/HADOOP-9295
> Project: Hadoop Common
> Issue Type: Bug
> Components: io
> Affects Versions: 1.0.3
> Reporter: David Parks
> Assignee: Karthik Kambatla
> Priority: Critical
> Attachments: MapWritableBugTest.java
>
>
> Verified the trunk looks the same as 1.0.3 for this issue.
> When mappers output MapWritables with different class types, then they are
> read in on the Reducer via an iterator (multiple calls to readFields without
> instantiating a new object) you'll get this:
> java.lang.IllegalArgumentException: Id 1 exists but maps to
> org.me.ClassTypeOne and not org.me.ClassTypeTwo
> at
> org.apache.hadoop.io.AbstractMapWritable.addToMap(AbstractMapWritable.java:73)
> at
> org.apache.hadoop.io.AbstractMapWritable.readFields(AbstractMapWritable.java:201)
> It happens because AbstractMapWritable accumulates class type entries in its
> ClassType to ID (and vice versa) hashmaps.
> Those accumulating classtype-to-id hashmaps need to be cleared to support
> multiple calls to readFields().
> I've attached a JUnit test that both demonstrates the problem and contains an
> embedded, fixed version of MapWritable and ArrayMapWritable (note the //TODO
> comments in the code where it was fixed in 2 places).
> If there's a better way to submit this recommended bug fix, someone please
> feel free to let me know.
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