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From "Simon Dircks (JIRA)" <j...@apache.org>
Subject [jira] Created: (MAPREDUCE-2378) Reduce fails when running on 1 small file.
Date Fri, 11 Mar 2011 23:20:03 GMT
Reduce fails when running on 1 small file. 

                 Key: MAPREDUCE-2378
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-2378
             Project: Hadoop Map/Reduce
          Issue Type: Bug
    Affects Versions: 0.21.0
         Environment: java version "1.6.0_07"
Diablo Java(TM) SE Runtime Environment (build 1.6.0_07-b02)
Diablo Java HotSpot(TM) 64-Bit Server VM (build 10.0-b23, mixed mode)

            Reporter: Simon Dircks

If i run the wordcount example on 1 small (less than 2MB) file i get the following error:

log4j:ERROR Failed to flush writer,
        at java.io.FileOutputStream.writeBytes(Native Method)
        at java.io.FileOutputStream.write(FileOutputStream.java:260)
        at sun.nio.cs.StreamEncoder.writeBytes(StreamEncoder.java:202)
        at sun.nio.cs.StreamEncoder.implFlushBuffer(StreamEncoder.java:272)
        at sun.nio.cs.StreamEncoder.implFlush(StreamEncoder.java:276)
        at sun.nio.cs.StreamEncoder.flush(StreamEncoder.java:122)
        at java.io.OutputStreamWriter.flush(OutputStreamWriter.java:212)
        at org.apache.log4j.helpers.QuietWriter.flush(QuietWriter.java:58)
        at org.apache.log4j.WriterAppender.subAppend(WriterAppender.java:316)
        at org.apache.log4j.WriterAppender.append(WriterAppender.java:160)
        at org.apache.hadoop.mapred.TaskLogAppender.append(TaskLogAppender.java:58)
        at org.apache.log4j.AppenderSkeleton.doAppend(AppenderSkeleton.java:251)
        at org.apache.log4j.helpers.AppenderAttachableImpl.appendLoopOnAppenders(AppenderAttachableImpl.java:66)
        at org.apache.log4j.Category.callAppenders(Category.java:206)
        at org.apache.log4j.Category.forcedLog(Category.java:391)
        at org.apache.log4j.Category.log(Category.java:856)
        at org.apache.commons.logging.impl.Log4JLogger.info(Log4JLogger.java:199)
        at org.apache.hadoop.mapreduce.task.reduce.ShuffleScheduler.freeHost(ShuffleScheduler.java:345)
        at org.apache.hadoop.mapreduce.task.reduce.Fetcher.run(Fetcher.java:152)

If i run the wordcount test with 2 files, it works fine. 

I have actually repeated this with my own code. I am working on something that requires me
to map/reduce a small file and I had to work around the problem by splitting the file into
2 1MB pieces for my job to run. 

All our jobs that run on 1 single larger file (over 1GB) work flawlessly. I am not exactly
sure the threshold, From the testing i have done it seems to be any file smaller than the
default HDFS block size (64MB) Sometimes it seems random in the 5-64MB range. But its 100%
for the 5MB and smaller files. 

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