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From "Ron Bodkin (JIRA)" <j...@apache.org>
Subject [jira] Commented: (AVRO-669) Avro Mapreduce Doesn't Work With Reflect Schemas
Date Wed, 06 Oct 2010 01:32:32 GMT

    [ https://issues.apache.org/jira/browse/AVRO-669?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12918376#action_12918376

Ron Bodkin commented on AVRO-669:

>From discussion on IRC, it'd be better to change the default values that ReflectData uses
when reading in types to be the values that are generated by the Avro code generator (e.g.,
it should use GenericData.Array rather than a Java array by default). 

This will also require encoding reflection data for arrays that used to be a default, e.g.,
the ReflectData.createSchema method should emit a CLASS_PROP of GenericArrayType.class and
reflect data reader should honor that.

> Avro Mapreduce Doesn't Work With Reflect Schemas
> ------------------------------------------------
>                 Key: AVRO-669
>                 URL: https://issues.apache.org/jira/browse/AVRO-669
>             Project: Avro
>          Issue Type: Bug
>            Reporter: Ron Bodkin
>            Assignee: Doug Cutting
>             Fix For: 1.5.0
>         Attachments: AVRO-669.patch, AVRO-669.patch.2
> 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)

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