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  1. Spark
  2. SPARK-18356

KMeans should cache RDD before training

    Details

    • Type: Improvement
    • Status: Resolved
    • Priority: Minor
    • Resolution: Fixed
    • Affects Version/s: 2.0.0, 2.0.1
    • Fix Version/s: 2.2.0
    • Component/s: ML
    • Labels:

      Description

      Hello,

      I'm newbie in spark, but I think that I found a small problem that can affect spark Kmeans performances.
      Before starting to explain the problem, I want to explain the warning that I faced.

      I tried to use Spark Kmeans with Dataframes to cluster my data

      df_Part = assembler.transform(df_Part)
      df_Part.cache()
      while (k<=max_cluster) and (wssse > seuilStop):
      kmeans = KMeans().setK(k)
      model = kmeans.fit(df_Part)
      wssse = model.computeCost(df_Part)
      k=k+1

      but when I run the code I receive the warning :
      WARN KMeans: The input data is not directly cached, which may hurt performance if its parent RDDs are also uncached.

      I searched in spark source code to find the source of this problem, then I realized there is two classes responsible for this warning:
      (mllib/src/main/scala/org/apache/spark/mllib/clustering/KMeans.scala )
      (mllib/src/main/scala/org/apache/spark/ml/clustering/KMeans.scala )

      When my dataframe is cached, the fit method transform my dataframe into an internally rdd which is not cached.
      Dataframe -> rdd -> run Training Kmeans Algo(rdd)

      -> The first class (ml package) responsible for converting the dataframe into rdd then call Kmeans Algorithm
      ->The second class (mllib package) implements Kmeans Algorithm, and here spark verify if the rdd is cached, if not a warning will be generated.

      So, the solution of this problem is to cache the rdd before running Kmeans Algorithm.
      https://github.com/ZakariaHili/spark/blob/master/mllib/src/main/scala/org/apache/spark/ml/clustering/KMeans.scala
      All what we need is to add two lines:
      Cache rdd just after dataframe transformation, then uncached it after training algorithm.

      I hope that I was clear.
      If you think that I was wrong, please let me know.

      Sincerely,
      Zakaria HILI

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            • Assignee:
              zahili zakaria hili
              Reporter:
              zahili zakaria hili
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