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From Amogh Vasekar <am...@yahoo-inc.com>
Subject Re: How to use MultipleTextOutputFormat ?
Date Tue, 27 Oct 2009 12:12:55 GMT
Hi,
The file name generated depends on the output <k,v> pair and hence, if you are modifying
the key from mapper to reducer output, collisions are possible. You may split and append 'name'
(* from part-*) to get unique reducer files, which can be merged later. Or see if multipleoutputs
fits your bill.
Hope this helps.

Amogh


On 10/27/09 4:04 PM, "tim robertson" <timrobertson100@gmail.com> wrote:

Hi all,

Using 0.20.1 I have a MultipleTextOutputFormat with the following:

  protected String generateFileNameForKeyValue(Object key, Object
value, String name) {
    return BASE_FILE + "/resource-" + key.toString();
  }

But when I run this on a 9 node cluster with 9 reducers I get issues
with nodes saying the file is already being created, and eventually
the job fails with half written output

Can someone please tell me if I am using this incorrectly? I suspect
it is because my reducer is generating a new key, so multiple reducers
are indeed creating the same file... could someone please verify this
suspicion?

Full stacktrace on a TT below.

Thanks,
Tim



2009-10-27 10:56:32,844 WARN org.apache.hadoop.mapred.TaskTracker:
Error running child
org.apache.hadoop.ipc.RemoteException:
org.apache.hadoop.hdfs.protocol.AlreadyBeingCreatedException: failed
to create file /user/root/delme2/resource-101 for
DFSClient_attempt_200910191701_0042_r_000005_1 on client 192.168.76.1,
bec
ause this file is already being created by
DFSClient_attempt_200910191701_0042_r_000005_2 on 192.168.76.3
        at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.startFileInternal(FSNamesystem.java:1064)
        at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.startFile(FSNamesystem.java:977)
        at org.apache.hadoop.hdfs.server.namenode.NameNode.create(NameNode.java:377)
        at sun.reflect.GeneratedMethodAccessor75.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:508)
        at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:959)
        at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:955)
        at java.security.AccessController.doPrivileged(Native Method)
        at javax.security.auth.Subject.doAs(Subject.java:396)
        at org.apache.hadoop.ipc.Server$Handler.run(Server.java:953)

        at org.apache.hadoop.ipc.Client.call(Client.java:739)
        at org.apache.hadoop.ipc.RPC$Invoker.invoke(RPC.java:220)
        at $Proxy1.create(Unknown Source)
        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.io.retry.RetryInvocationHandler.invokeMethod(RetryInvocationHandler.java:82)
        at org.apache.hadoop.io.retry.RetryInvocationHandler.invoke(RetryInvocationHandler.java:59)
        at $Proxy1.create(Unknown Source)
        at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream.<init>(DFSClient.java:2674)
        at org.apache.hadoop.hdfs.DFSClient.create(DFSClient.java:488)
        at org.apache.hadoop.hdfs.DistributedFileSystem.create(DistributedFileSystem.java:195)
        at org.apache.hadoop.fs.FileSystem.create(FileSystem.java:479)
        at org.apache.hadoop.fs.FileSystem.create(FileSystem.java:379)
        at org.apache.hadoop.mapred.TextOutputFormat.getRecordWriter(TextOutputFormat.java:121)
        at org.apache.hadoop.mapred.lib.MultipleTextOutputFormat.getBaseRecordWriter(MultipleTextOutputFormat.java:44)
        at org.apache.hadoop.mapred.lib.MultipleOutputFormat$1.write(MultipleOutputFormat.java:99)
        at org.apache.hadoop.mapred.ReduceTask$3.collect(ReduceTask.java:440)
        at org.gbif.occurrencestore.mapreduce.classification.ClassificationMapReduce$Transpose.reduce(ClassificationMapReduce.java:203)
        at org.gbif.occurrencestore.mapreduce.classification.ClassificationMapReduce$Transpose.reduce(ClassificationMapReduce.java:191)
        at org.apache.hadoop.mapred.ReduceTask.runOldReducer(ReduceTask.java:463)
        at org.apache.hadoop.mapred.ReduceTask.run(ReduceTask.java:411)
        at org.apache.hadoop.mapred.Child.main(Child.java:170)


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