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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