[jira] [Created] (HADOOP-9295) AbstractMapWritable throws exception when calling readFields() multiple times when the maps contain different class types

["David Parks (JIRA)" <ji...@apache.org>]

David Parks created HADOOP-9295:
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             Summary: 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
            Priority: Critical


Verified the trunk looks the same as 1.0.3 for this issue.

When you save two different class types two MapWritables, then try to read them in on the Reducer over 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 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).


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