'_partition.lst' does not exist error - hadoop

Question

I tried to use 'RandomSampler' to partition the mapper results. And here're the related codes:
JobConf conf = new JobConf(SortExample.class);
conf.setJobName("sortexample");
...
conf.setPartitionerClass(TotalOrderPartitioner.class);
InputSampler.Sampler<IntWritable, Text> sampler =
new InputSampler.RandomSampler<IntWritable, Text>(0.1, 100);
InputSampler.writePartitionFile(conf, sampler);
conf.setNumReduceTasks(2);
In my understanding, the sampler will write into a file called, by default, _patition.lst describing the partition that the job will automatically use to decide which key/value pairs to send to which reducers.
But after running, I got the following error:
ava.lang.RuntimeException: Error in configuring object
at org.apache.hadoop.util.ReflectionUtils.setJobConf(ReflectionUtils.java:93)
at org.apache.hadoop.util.ReflectionUtils.setConf(ReflectionUtils.java:64)
at org.apache.hadoop.util.ReflectionUtils.newInstance(ReflectionUtils.java:117)
at org.apache.hadoop.mapred.MapTask$OldOutputCollector.<init>(MapTask.java:574)
at org.apache.hadoop.mapred.MapTask.runOldMapper(MapTask.java:436)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:372)
at org.apache.hadoop.mapred.Child$4.run(Child.java:255)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:396)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1083)
at org.apache.hadoop.mapred.Child.main(Child.java:249)
Caused by: java.lang.reflect.InvocationTargetException
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.ReflectionUtils.setJobConf(ReflectionUtils.java:88)
... 10 more
Caused by: java.lang.IllegalArgumentException: Can't read partitions file
at org.apache.hadoop.mapred.lib.TotalOrderPartitioner.configure(TotalOrderPartitioner.java:91)
... 15 more
Caused by: java.io.FileNotFoundException: File _partition.lst does not exist.
And I didn't know where the file '_partition.lst' is? There must be some mis-understanding here, and I appreciate any helps~

Answer 1

I think you need to call getSample() on one of the InputSample inner classes. That's what reads a file via an InputFormat and actually figures out what splits should go into the _partition.lst file.