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https://issues.apache.org/jira/browse/SPARK-18356?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Joseph K. Bradley updated SPARK-18356:
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Summary: KMeans should cache RDD before training (was: Issue + Resolution:
Kmeans Spark Performances (ML package))
> KMeans should cache RDD before training
> ---------------------------------------
>
> Key: SPARK-18356
> URL: https://issues.apache.org/jira/browse/SPARK-18356
> Project: Spark
> Issue Type: Improvement
> Components: ML
> Affects Versions: 2.0.0, 2.0.1
> Reporter: zakaria hili
> Assignee: zakaria hili
> Priority: Minor
> Labels: easyfix
> Fix For: 2.2.0
>
>
> 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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