Gabriel Reid created CRUNCH-539:
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Summary: Use of TupleWritable.setConf fails in mapper/reducer
Key: CRUNCH-539
URL: https://issues.apache.org/jira/browse/CRUNCH-539
Project: Crunch
Issue Type: Bug
Affects Versions: 0.12.0
Reporter: Gabriel Reid
In (at least) more recent versions of Hadoop 2, the implicit call to
TupleWritable.setConf that happens when using TupleWritables fails with a
ClassNotFoundException for (ironically) the TupleWritable class.
This appears to be due to the way that ObjectInputStream resolves classes in
its [resolveClass
method|https://docs.oracle.com/javase/7/docs/api/java/io/ObjectInputStream.html#resolveClass(java.io.ObjectStreamClass)],
together with the way that the context classloader is set within a hadoop
mapper or reducer.
This is similar to PIG-2532.
This can be reproduced in the local job tracker (at least) in Hadoop 2.7.0, but
it can't be reproduced in Crunch integration tests (due to classloading setup).
It appears that this issue is only present in Crunch 0.12.
The following code within a simple pipeline will cause this issue to occur:
{code}
PTable<String, Integer> yearTemperatures = ... /* Writable-based PTable */
PTable<String, Integer> maxTemps = yearTemperatures
.groupByKey()
.combineValues(Aggregators.MAX_INTS())
.top(1); //LINE THAT CAUSES THE ERROR
{code}
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