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From Lewis John Mcgibbney <lewis.mcgibb...@gmail.com>
Subject Should MongoDB know about Utf8?
Date Thu, 09 Oct 2014 18:44:21 GMT
Hi Folks,
Whilst in the muddle of upgrading Nutch 2.3-SNAPSHOT to use Gora 0.5 we've
run into a problem when implementing the gora-mongodb stuff.
The issue is described within the Jira issue [0]. This being said, Kiril
(CC'd) has stated quite clearly why this is happening. This is a
consequence of the following lines of the Nutch code base

https://github.com/apache/nutch/blob/2.x/src/java/org/apache/nutch/fetcher/FetcherJob.java#L218

https://github.com/apache/nutch/blob/2.x/src/java/org/apache/nutch/parse/ParserJob.java#L274

https://github.com/apache/nutch/blob/2.x/src/java/org/apache/nutch/crawl/DbUpdaterJob.java#L128

and results in the following stack trace

java.lang.IllegalArgumentException: can't serialize class
org.apache.avro.util.Utf8
at org.bson.BasicBSONEncoder._putObjectField(BasicBSONEncoder.java:284)
at org.bson.BasicBSONEncoder.putObject(BasicBSONEncoder.java:185)
at org.bson.BasicBSONEncoder.putObject(BasicBSONEncoder.java:131)
at com.mongodb.DefaultDBEncoder.writeObject(DefaultDBEncoder.java:33)
at com.mongodb.OutMessage.putObject(OutMessage.java:289)
at com.mongodb.OutMessage.writeQuery(OutMessage.java:211)
at com.mongodb.OutMessage.query(OutMessage.java:86)
at com.mongodb.DBCollectionImpl.find(DBCollectionImpl.java:81)
at com.mongodb.DBCollectionImpl.find(DBCollectionImpl.java:66)
at com.mongodb.DBCursor._check(DBCursor.java:458)
at com.mongodb.DBCursor._hasNext(DBCursor.java:546)
at com.mongodb.DBCursor.hasNext(DBCursor.java:571)
at
org.apache.gora.mongodb.query.MongoDBResult.nextInner(MongoDBResult.java:69)
at org.apache.gora.query.impl.ResultBase.next(ResultBase.java:114)
at
org.apache.gora.mapreduce.GoraRecordReader.nextKeyValue(GoraRecordReader.java:119)
at
org.apache.hadoop.mapred.MapTask$NewTrackingRecordReader.nextKeyValue(MapTask.java:531)
at org.apache.hadoop.mapreduce.MapContext.nextKeyValue(MapContext.java:67)
at org.apache.hadoop.mapreduce.Mapper.run(Mapper.java:144)
at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:764)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:364)
at
org.apache.hadoop.mapred.LocalJobRunner$Job$MapTaskRunnable.run(LocalJobRunner.java:223)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
at java.util.concurrent.FutureTask.run(FutureTask.java:262)
at
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:744)

The cause is the following line (example from FetcherJob):
filter.getOperands().add(new Utf8(batchId));

During serialization MongoDB doesn't know about Utf8 type.
My question is now... should we remove the Utf8 from Nutch, or should
gora-mongodb handle this silently?

Thanks for reading.
Lewis

[0] https://issues.apache.org/jira/browse/NUTCH-1843

-- 
*Lewis*

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