Hi Jane, The default Reducer (IdentityReducer) would simply read/write everything that goes through it. By default Shuffling would also happen and the map output data is partitioned by the HashPartitioner.
If you don't need the shuffle/reduce, you need to explicitly set the number of the reduce tasks to zero via JobConf's setNumReduceTasks(int num). Hope that helps. Jie On Wed, Mar 7, 2012 at 11:28 PM, Jane Wayne <jane.wayne2...@gmail.com>wrote: > i have a Mapper and Reducer as a part of a job. all my data transformation > occurs in the mapper, and there is absolutely nothing that needs to be done > in the reducer. when i set the reducer on the Job, i simply use the > Reducer.class. > > i notice that after the mapper tasks have reached 100%, then the time until > reducing starts is very long. when reducing starts then i get a > java.io.IOException: No space left on deviceFSError. i checked the dfs > health (via web page), and i still have 42.41% DFS remaining. why does this > occur? i see that eventually 4 attempts are made to call Reducer, however, > they all end up with the IOException mentioned. at the bottom is an output. > notice that the percentage goes up then back down to 0% before the > IOException. > > also, i want to know if i can just subclass Reducer or do something about > shuffling and sorting as these steps are not important. i just want each > record emitted from the Mapper to go straight to disk. is it possible to do > this without going through Reducer? i am thinking this is part of the > problem for taking so long between 100% map and the first sign of reduce. > > EXAMPLE OUTPUT > > 12/03/07 22:38:45 INFO mapred.JobClient: map 98% reduce 0% > 12/03/07 22:39:18 INFO mapred.JobClient: map 99% reduce 0% > 12/03/07 22:39:43 INFO mapred.JobClient: map 100% reduce 0% > 12/03/07 22:58:14 INFO mapred.JobClient: map 100% reduce 1% > 12/03/07 22:58:23 INFO mapred.JobClient: map 100% reduce 3% > 12/03/07 22:58:38 INFO mapred.JobClient: map 100% reduce 6% > 12/03/07 22:58:57 INFO mapred.JobClient: map 100% reduce 7% > 12/03/07 22:59:21 INFO mapred.JobClient: map 100% reduce 9% > 12/03/07 23:00:00 INFO mapred.JobClient: map 100% reduce 10% > 12/03/07 23:00:09 INFO mapred.JobClient: map 100% reduce 12% > 12/03/07 23:00:58 INFO mapred.JobClient: map 100% reduce 0% > 12/03/07 23:01:00 INFO mapred.JobClient: Task Id : > attempt_201203071517_0043_r_000000_0, Status : FAILED > FSError: java.io.IOException: No space left on deviceFSError: > java.io.IOException: No space left on deviceFSError: java.io.IOException: > No space left on deviceFSError: java.io.IOException: No space left on > deviceFSError: java.io.IOException: No space left on deviceFSError: > java.io.IOException: No space left on device > attempt_201203071517_0043_r_000000_0: log4j:ERROR Failed to flush writer, > attempt_201203071517_0043_r_000000_0: java.io.IOException: No space left on > device > 12/03/07 23:01:31 INFO mapred.JobClient: map 100% reduce 1% > 12/03/07 23:01:34 INFO mapred.JobClient: map 100% reduce 3% > 12/03/07 23:01:37 INFO mapred.JobClient: map 100% reduce 4% > 12/03/07 23:01:49 INFO mapred.JobClient: map 100% reduce 6% > 12/03/07 23:01:55 INFO mapred.JobClient: map 100% reduce 7% > 12/03/07 23:02:19 INFO mapred.JobClient: map 100% reduce 9% > 12/03/07 23:02:52 INFO mapred.JobClient: map 100% reduce 0% > 12/03/07 23:02:54 INFO mapred.JobClient: Task Id : > attempt_201203071517_0043_r_000000_1, Status : FAILED > FSError: java.io.IOException: No space left on deviceFSError: > java.io.IOException: No space left on deviceFSError: java.io.IOException: > No space left on device >
