[AVRO-669] Avro Mapreduce Doesn't Work With Reflect Schemas

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.5.0
• Component/s: java
• Assignee: Doug Cutting
• Reporter: Ron Bodkin
• Created: 17/Sep/10 05:46
• Updated: 27/Mar/12 06:29
• Resolved: 29/Dec/10 21:38

Description

I'm trying to get the Avro trunk code (from Subversion) to work with a simple example of a reflection-defined schema, using a class I created. I use a ReflectDatumWriter to write a set of records to a file, e.g.,

DatumWriter writer = new ReflectDatumWriter(Record.class);
DataFileWriter file = new DataFileWriter(writer);

However, when I try to read that data in using an AvroMapper it fails with an exception as shown below. It turns out that the mapreduce implementation hard-codes a dependence on SpecificDatum readers and writers.

I've tested switching to use ReflectDatum instead in five places to try to get it to work for an end-to-end reflect data example:
AvroFileInputFormat
AvroFileOutputFormat
AvroSerialization (getDeserializer and getSerializer)
AvroKeyComparator

However, switching to use reflection for AvroKeyComparator doesn't work:
java.lang.UnsupportedOperationException
at org.apache.avro.reflect.ReflectData.compare(ReflectData.java:427)
at org.apache.avro.mapred.AvroKeyComparator.compare(AvroKeyComparator.java:46)

It should be possible to implement compare on reflect data (just like GenericData's implementation but use the field name instead (or better yet a cached java.lang.reflect.Field)...

Original exception:
java.lang.ClassCastException: tba.mr.sample.avro.Record cannot be cast to org.apache.avro.generic.IndexedRecord
at org.apache.avro.generic.GenericDatumReader.setField(GenericDatumReader.java:152)
at org.apache.avro.generic.GenericDatumReader.readRecord(GenericDatumReader.java:142)
at org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:114)
at org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:105)
at org.apache.avro.file.DataFileStream.next(DataFileStream.java:198)
at org.apache.avro.mapred.AvroRecordReader.next(AvroRecordReader.java:63)
at org.apache.avro.mapred.AvroRecordReader.next(AvroRecordReader.java:33)
at org.apache.hadoop.mapred.MapTask$TrackedRecordReader.moveToNext(MapTask.java:192)
at org.apache.hadoop.mapred.MapTask$TrackedRecordReader.next(MapTask.java:176)
at org.apache.hadoop.mapred.MapRunner.run(MapRunner.java:48)
at org.apache.hadoop.mapred.MapTask.runOldMapper(MapTask.java:358)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:307)
at org.apache.hadoop.mapred.Child.main(Child.java:170)

Issue Links

• is related to: AVRO-638 make reflect, specific and generic data compatible