You may consider "SpecificRecord" or "GenericRecord" of Avor. Yong
Date: Fri, 7 Mar 2014 10:29:49 +0800 Subject: Re: MapReduce: How to output multiplt Avro files? From: raofeng...@gmail.com To: user@hadoop.apache.org; ha...@cloudera.com thanks, Harsh. any idea on how to build a common map output data type? The only way I can think of is "toString()", which would be very inefficient, since A and B are big objects and may change with time, which is also the reason we want to use Avro serialization. 2014-03-07 9:55 GMT+08:00 Harsh J <ha...@cloudera.com>: If you have a reducer involved, you'll likely need a common map output data type that both A and B can fit into. On Thu, Mar 6, 2014 at 12:09 AM, Fengyun RAO <raofeng...@gmail.com> wrote: > 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. -- Harsh J
