Defining schema for Avro key in Oozie - hadoop

Question

I'm new to map reduce and Avro. My project basically has only mapper function that takes in Text data and outputs Avro data and for that I've declared my mapper something like:
public class AvroMapper extends Mapper(LongWritable, Text, AvroKey<CharSequence>, NullWritable)
I'm having troubles setting the schema for key in Oozie workflow. My Oozie file config is:
<property>
<name>mapred.output.key.class</name>
<value>org.apache.avro.mapred.NullWriatable</value>
</property>
<property>
<name>mapred.mapoutput.key.class</name>
<value>org.apache.avro.mapred.AvroKey</value>
</property>
<property>
<name>mapred.mapoutput.value.class</name>
<value>org.apache.avro.mapred.NullWritable</value>
</property>
<property>
<name>mapred.output.key.comparator.class</name>
<value>org.apache.avro.mapred.AvroKeyComparator</value>
</property>
<property>
<name>avro.schema.output.key</name>
<value>{my JSON schema}</value>
</property>
<property>
<name>mapreduce.inputformat.class</name>
<value>org.apache.hadoop.mapreduce.lib.input.TextInputFormat</value>
</property>
<property>
<name>mapreduce.outputformat.class</name>
<value>org.apache.avro.mapreduce.AvroKeyOutputFormat</value>
</property>
but it still throws:
java.lang.NullPointerException
at org.apache.avro.mapred.Pair.getKeySchema(Pair.java:68)
at org.apache.avro.mapred.AvroKeyComparator.setConf(AvroKeyComparator.java:39)
at org.apache.hadoop.util.ReflectionUtils.setConf(ReflectionUtils.java:73)
at org.apache.hadoop.util.ReflectionUtils.newInstance(ReflectionUtils.java:133)
at org.apache.hadoop.mapred.JobConf.getOutputKeyComparator(JobConf.java:818)
at org.apache.hadoop.mapred.MapTask$MapOutputBuffer.init(MapTask.java:836)
at org.apache.hadoop.mapred.MapTask.createSortingCollector(MapTask.java:376)
at org.apache.hadoop.mapred.MapTask.access$100(MapTask.java:85)
at org.apache.hadoop.mapred.MapTask$NewOutputCollector.<init>(MapTask.java:584)
at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:656)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:330)
at org.apache.hadoop.mapred.Child$4.run(Child.java:268)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:396)
at org.apache.ha...
Please guide me where am I going wrong..

Answer 1

Use AvroMapper and AvroReducer classes instead. It goes easier this way for me. An please remember to use Pair class and schema in this case.
Anyway Oozie configuration for Avro is not trivial. To save you some time here is my config for AvroMapper and AvroReducer:
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<configuration>
<property>
<name>avro.input.schema</name>
<value>{"type":"record","name":"Pair","namespace":"org.apache.avro.mapred","fields":[... your fields ...]}</value>
</property>
<property>
<name>avro.output.schema</name>
<value>{"type":"record","name":"Pair","namespace":"org.apache.avro.mapred","fields":[... your fields ...]}</value>
</property>
<property>
<name>avro.mapper</name>
<value>your.mapper.class.Name</value>
</property>
<property>
<name>avro.reducer</name>
<value>your.reducer.class.Name</value>
</property>
<property>
<name>mapred.output.key.comparator.class</name>
<value>org.apache.avro.mapred.AvroKeyComparator</value>
</property>
<property>
<name>mapred.reducer.class</name>
<value>org.apache.avro.mapred.HadoopReducer</value>
</property>
<property>
<name>mapred.output.format.class</name>
<value>org.apache.avro.mapred.AvroOutputFormat</value>
</property>
<property>
<name>mapred.mapper.class</name>
<value>org.apache.avro.mapred.HadoopMapper</value>
</property>
<property>
<name>mapred.input.format.class</name>
<value>org.apache.avro.mapred.AvroInputFormat</value>
</property>
<property>
<name>mapred.output.key.class</name>
<value>org.apache.avro.mapred.AvroWrapper</value>
</property>
<property>
<name>mapred.mapoutput.value.class</name>
<value>org.apache.avro.mapred.AvroValue</value>
</property>
<property>
<name>io.serializations</name>
<value>org.apache.hadoop.io.serializer.WritableSerialization,org.apache.avro.mapred.AvroSerialization</value>
</property>
<property>
<name>mapred.mapoutput.key.class</name>
<value>org.apache.avro.mapred.AvroKey</value>
</property>
</configuration>