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Posted to issues@spark.apache.org by "Sean R. Owen (Jira)" <ji...@apache.org> on 2019/11/13 14:17:00 UTC
[jira] [Resolved] (SPARK-29823) Improper persist strategy in
mllib.clustering.KMeans.run()
[ https://issues.apache.org/jira/browse/SPARK-29823?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Sean R. Owen resolved SPARK-29823.
----------------------------------
Fix Version/s: 3.0.0
Resolution: Fixed
Issue resolved by pull request 26483
[https://github.com/apache/spark/pull/26483]
> Improper persist strategy in mllib.clustering.KMeans.run()
> ----------------------------------------------------------
>
> Key: SPARK-29823
> URL: https://issues.apache.org/jira/browse/SPARK-29823
> Project: Spark
> Issue Type: Bug
> Components: MLlib
> Affects Versions: 2.4.3
> Reporter: Dong Wang
> Assignee: Aman Omer
> Priority: Major
> Fix For: 3.0.0
>
>
> In mllib.clustering.KMeans.run(), the rdd {color:#de350b}_norms_{color} is persisted. But {color:#de350b}_norms_ {color}only has a single child, i.e., the rdd {color:#de350b}_zippedData_ {color:#172b4d}which was not persisted{color}{color}{color:#172b4d}.{color} So all the actions that reply on _norms_ also reply on _{color:#de350b}zippedData{color}._ The rdd {color:#de350b}_zippedData_{color} will be used by multiple times in _runAlgorithm()._ Therefore _{color:#de350b}zippedData{color}_ should be persisted, not _{color:#de350b}norms{color}_.
> {code:scala}
> private[spark] def run(
> data: RDD[Vector],
> instr: Option[Instrumentation]): KMeansModel = {
> if (data.getStorageLevel == StorageLevel.NONE) {
> logWarning("The input data is not directly cached, which may hurt performance if its"
> + " parent RDDs are also uncached.")
> }
> // Compute squared norms and cache them.
> val norms = data.map(Vectors.norm(_, 2.0))
> norms.persist() // Unnecessary persist. Only used to generate zippedData.
> val zippedData = data.zip(norms).map { case (v, norm) =>
> new VectorWithNorm(v, norm)
> } // needs to persist
> val model = runAlgorithm(zippedData, instr)
> norms.unpersist() // Change to zippedData.unpersist()
> {code}
> This issue is reported by our tool CacheCheck, which is used to dynamically detecting persist()/unpersist() api misuses.
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