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https://issues.apache.org/jira/browse/CRUNCH-339?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13891645#comment-13891645
 ] 

Micah Whitacre commented on CRUNCH-339:
---------------------------------------

If your DoFn is like your example (no holding onto any references and an 
anonymous inner class) the issue might be that the containing class is not 
serializable.  That is called out in the guide Josh references as well.

> java.io.NotSerializableException when calling PCollection.cache()
> -----------------------------------------------------------------
>
>                 Key: CRUNCH-339
>                 URL: https://issues.apache.org/jira/browse/CRUNCH-339
>             Project: Crunch
>          Issue Type: Bug
>          Components: IO
>    Affects Versions: 0.8.2
>         Environment: CDH4.4.0
>            Reporter: Sungwoo Park
>
> When I was debugging a MRPipeline, I found that calling cache() function 
> causes java.io.NotSerializableException
> Code:
> (...)
> PCollection<Long> candidates = loadCandidate(pipeline, candidatesPath);
> candidates.cache();
> (...)
> public PCollection<Long> loadCandidate(Pipeline p, Path candidatesPath) {
>               if(candidatesPath == null)
>                       return null;
>               
>               return p.read(From.textFile(candidatesPath)).parallelDo(new 
> DoFn<String, Long>(){
>                       @Override
>                       public void process(String stringId, Emitter<Long> 
> emitter) {
>                               emitter.emit(Long.parseLong(stringId));
>                       }
>                       
>               }, Writables.longs());
>       }
> Stack trace:
> Exception in thread "main" org.apache.crunch.CrunchRuntimeException: 
> java.io.NotSerializableException: 
> com.coupang.recommender.ever.utils.recommender.OryxRecommender
>       at org.apache.crunch.impl.mr.MRPipeline.plan(MRPipeline.java:104)
>       at org.apache.crunch.impl.mr.MRPipeline.runAsync(MRPipeline.java:123)
>       at org.apache.crunch.impl.mr.MRPipeline.run(MRPipeline.java:111)
>       at 
> org.apache.crunch.impl.dist.DistributedPipeline.done(DistributedPipeline.java:109)
>       at 
> com.coupang.recommender.ever.utils.recommender.OryxRecommender.run(OryxRecommender.java:108)
>       at com.coupang.recommender.ever.utils.EverUtil.run(EverUtil.java:30)
>       at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:70)
>       at com.coupang.recommender.ever.utils.Driver.main(Driver.java:34)
>       at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
>       at 
> sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
>       at 
> sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
>       at java.lang.reflect.Method.invoke(Method.java:597)
>       at org.apache.hadoop.util.RunJar.main(RunJar.java:208)
> Caused by: java.io.NotSerializableException: 
> com.coupang.recommender.ever.utils.recommender.OryxRecommender
>       at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1164)
>       at 
> java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1518)
>       at 
> java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1483)
>       at 
> java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1400)
>       at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1158)
>       at 
> java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1518)
>       at 
> java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1483)
>       at 
> java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1400)
>       at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1158)
>       at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:330)
>       at java.util.ArrayList.writeObject(ArrayList.java:570)
>       at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
>       at 
> sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
>       at 
> sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
>       at java.lang.reflect.Method.invoke(Method.java:597)
>       at 
> java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:940)
>       at 
> java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1469)
>       at 
> java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1400)
>       at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1158)
>       at 
> java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1518)
>       at 
> java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1483)
>       at 
> java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1400)
>       at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1158)
>       at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:330)
>       at java.util.ArrayList.writeObject(ArrayList.java:570)
>       at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
>       at 
> sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
>       at 
> sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
>       at java.lang.reflect.Method.invoke(Method.java:597)
>       at 
> java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:940)
>       at 
> java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1469)
>       at 
> java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1400)
>       at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1158)
>       at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:330)
>       at org.apache.crunch.util.DistCache.write(DistCache.java:55)
>       at 
> org.apache.crunch.impl.mr.plan.JobPrototype.serialize(JobPrototype.java:242)
>       at 
> org.apache.crunch.impl.mr.plan.JobPrototype.build(JobPrototype.java:215)
>       at 
> org.apache.crunch.impl.mr.plan.JobPrototype.getCrunchJob(JobPrototype.java:134)
>       at org.apache.crunch.impl.mr.plan.MSCRPlanner.plan(MSCRPlanner.java:165)
>       at org.apache.crunch.impl.mr.MRPipeline.plan(MRPipeline.java:102)
>       ... 12 more



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