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Posted to mapreduce-dev@hadoop.apache.org by "Ruibang He (JIRA)" <ji...@apache.org> on 2009/11/30 10:47:20 UTC

[jira] Created: (MAPREDUCE-1248) Redundant memory copying in StreamKeyValUtil

Redundant memory copying in StreamKeyValUtil
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                 Key: MAPREDUCE-1248
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1248
             Project: Hadoop Map/Reduce
          Issue Type: Improvement
          Components: contrib/streaming
            Reporter: Ruibang He
            Priority: Minor


I found that when MROutputThread collecting the output of  Reducer, it calls StreamKeyValUtil.splitKeyVal() and two local byte-arrays are allocated there for each line of output. Later these two byte-arrays are passed to variable key and val. There are twice memory copying here, one is the System.arraycopy() method, the other is inside key.set() / val.set().

This causes double times of memory copying for the whole output (may lead to higher CPU consumption), and frequent temporay object allocation.

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