[jira] [Created] (SPARK-21624) Optimize communication cost of RF/GBT/DT

["Peng Meng (JIRA)" <ji...@apache.org>]

Peng Meng created SPARK-21624:
---------------------------------

             Summary: Optimize communication cost of RF/GBT/DT
                 Key: SPARK-21624
                 URL: https://issues.apache.org/jira/browse/SPARK-21624
             Project: Spark
          Issue Type: Improvement
          Components: ML, MLlib
    Affects Versions: 2.3.0
            Reporter: Peng Meng


{quote}The implementation of RF is bound by either  the cost of statistics computation on workers or by communicating the sufficient statistics.{quote}

The statistics are stored in allStats:

{code:java}
  /**
   * Flat array of elements.
   * Index for start of stats for a (feature, bin) is:
   *   index = featureOffsets(featureIndex) + binIndex * statsSize
   */
  private var allStats: Array[Double] = new Array[Double](allStatsSize)
{code}
The size of allStats maybe very large, and it can be very spare, especially on the nodes that near the leave of the tree. 

I have changed allStats from Array to SparseVector,  my tests show the communication is down by about 50%.




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