[jira] [Created] (MAPREDUCE-4883) Reducer's Maximum Shuffle Buffer Size should be enlarged for 64bit JVM

["Lijie Xu (JIRA)" <ji...@apache.org>]

Lijie Xu created MAPREDUCE-4883:
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             Summary: Reducer's Maximum Shuffle Buffer Size should be enlarged for 64bit JVM
                 Key: MAPREDUCE-4883
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-4883
             Project: Hadoop Map/Reduce
          Issue Type: Improvement
    Affects Versions: 1.0.3, 0.20.2
         Environment: Especially for 64bit JVM
            Reporter: Lijie Xu


In hadoop-0.20.2, hadoop-1.0.3 or other versions, reducer's shuffle buffer size cannot exceed 2048MB (i.e., Integer.MAX_VALUE). This is reasonable for 32bit JVM.
But for 64bit JVM, although reducer's JVM size can be set more than 2048MB (e.g., mapred.child.java.opts=-Xmx4000m), the heap size used for shuffle buffer is at most "2048MB * maxInMemCopyUse (default 0.7)" not "4000MB * maxInMemCopyUse". 

So the pointed piece of code in ReduceTask.java needs modification for 64bit JVM.
---------------------------------------------------------------------------------------
      private final long maxSize;
      private final long maxSingleShuffleLimit;
     
      private long size = 0;
     
      private Object dataAvailable = new Object();
      private long fullSize = 0;
      private int numPendingRequests = 0;
      private int numRequiredMapOutputs = 0;
      private int numClosed = 0;
      private boolean closed = false;
     
      public ShuffleRamManager(Configuration conf) throws IOException {
        final float maxInMemCopyUse =
          conf.getFloat("mapred.job.shuffle.input.buffer.percent", 0.70f);
        if (maxInMemCopyUse > 1.0 || maxInMemCopyUse < 0.0) {
          throw new IOException("mapred.job.shuffle.input.buffer.percent" +
                                maxInMemCopyUse);
        }
        // Allow unit tests to fix Runtime memory
-->   maxSize = (int)(conf.getInt("mapred.job.reduce.total.mem.bytes",
-->        (int)Math.min(Runtime.getRuntime().maxMemory(), Integer.MAX_VALUE))
-->      * maxInMemCopyUse);
        maxSingleShuffleLimit = (long)(maxSize * MAX_SINGLE_SHUFFLE_SEGMENT_FRACTION);
        LOG.info("ShuffleRamManager: MemoryLimit=" + maxSize +
                 ", MaxSingleShuffleLimit=" + maxSingleShuffleLimit);
      }


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