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

["Todd Lipcon (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/MAPREDUCE-4883?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13534242#comment-13534242 ] 

Todd Lipcon commented on MAPREDUCE-4883:
----------------------------------------

I believe, even in a 64-bit JVM, the max array size is Integer.MAX_VALUE (2GB)
                
> 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: 0.20.2, 1.0.3
>         Environment: Especially for 64bit JVM
>            Reporter: Lijie Xu
>              Labels: patch
>   Original Estimate: 12h
>  Remaining Estimate: 12h
>
> 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);
>       }

--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira