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From Fengyun RAO <raofeng...@gmail.com>
Subject Re: MapReduce: How to output multiplt Avro files?
Date Fri, 07 Mar 2014 07:15:02 GMT
thanks, Alan, it works!


2014-03-07 11:21 GMT+08:00 Alan Paulsen <phearm@gmail.com>:

> Hi Fengyun,
>
>
>
> Here's what I've done in the past when facing a similar issue:
>
>
>
> 1)      Set the map output schema to a UNION of both of your target
> schemas, A and B.
>
> 2)      Serialize the data in the mappers, using the avro datum as the
> value.
>
> 3)      Figure out what the avro schema is for each datum and write out
> the data in the reducer.
>
>
>
> Thanks,
>
>
>
> Alan
>
>
>
> *From:* Fengyun RAO [mailto:raofengyun@gmail.com]
> *Sent:* Thursday, March 06, 2014 2:14 AM
> *To:* user@hadoop.apache.org; user@avro.apache.org
> *Subject:* Re: MapReduce: How to output multiplt Avro files?
>
>
>
> add avro user mail-list
>
>
>
> 2014-03-06 16:09 GMT+08:00 Fengyun RAO <raofengyun@gmail.com>:
>
> our input is a line of text which may be parsed to e.g. A or B object.
>
> We want all A objects written to "A.avro" files, while all B objects
> written to "B.avro".
>
>
>
> I looked into AvroMultipleOutputs class:
> http://avro.apache.org/docs/1.7.4/api/java/org/apache/avro/mapreduce/AvroMultipleOutputs.html
>
> There is an example, however, it's not quite clear.
>
> For job submission, it uses AvroMultipleOutputs.addNamedOutput to add
> schemas for A and B.
>
> In my program looks like:
>
>         AvroMultipleOutputs.addNamedOutput(job, "A",
> AvroKeyOutputFormat.class, aSchema, null);
>
>         AvroMultipleOutputs.addNamedOutput(job, "B",
> AvroKeyOutputFormat.class, bSchema, null);
>
> I believe this is for Reducer output files.
>
>
>
> *My question is* what the Mapper output should be, in specific what
> "job.setMapOutputValueClass" should be,
>
> since the Mapper output could be A or B object, with schema aSchema or
> bSchema.
>
>
>
> In my progam, I simply set it to GenericData, but get error as below:
>
>
>
> 14/03/06 15:55:34 INFO mapreduce.Job: Task Id :
> attempt_1393817780522_0012_m_000010_2, Status : FAILED
>
> Error: java.lang.NullPointerException
>
>         at
> org.apache.hadoop.mapred.MapTask$MapOutputBuffer.init(MapTask.java:989)
>
>         at
> org.apache.hadoop.mapred.MapTask.createSortingCollector(MapTask.java:390)
>
>         at org.apache.hadoop.mapred.MapTask.access$100(MapTask.java:79)
>
>         at
> org.apache.hadoop.mapred.MapTask$NewOutputCollector.<init>(MapTask.java:674)
>
>         at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:746)
>
>         at org.apache.hadoop.mapred.MapTask.run(MapTask.java:339)
>
>         at org.apache.hadoop.mapred.YarnChild$2.run(YarnChild.java:165)
>
>         at java.security.AccessController.doPrivileged(Native Method)
>
>         at javax.security.auth.Subject.doAs(Subject.java:415)
>
>         at
> org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1491)
>
>         at org.apache.hadoop.mapred.YarnChild.main(YarnChild.java:160)
>
>
>
> I have no idea what this means.
>
>
>

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