[jira] [Updated] (SPARK-29813) Missing persist in mllib.PrefixSpan.findFrequentItems()

["Aman Omer (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SPARK-29813?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Aman Omer updated SPARK-29813:
------------------------------
        Parent: SPARK-29818
    Issue Type: Sub-task  (was: Improvement)

> Missing persist in mllib.PrefixSpan.findFrequentItems()
> -------------------------------------------------------
>
>                 Key: SPARK-29813
>                 URL: https://issues.apache.org/jira/browse/SPARK-29813
>             Project: Spark
>          Issue Type: Sub-task
>          Components: MLlib
>    Affects Versions: 2.4.3
>            Reporter: Dong Wang
>            Priority: Major
>
> There are three actions in this piece of code: reduceByKey, sortBy, and collect. But data is not persisted, which will cause recomputation.
> {code:scala}
>   private[fpm] def findFrequentItems[Item: ClassTag](
>       data: RDD[Array[Array[Item]]],
>       minCount: Long): Array[Item] = {
>     data.flatMap { itemsets =>
>       val uniqItems = mutable.Set.empty[Item]
>       itemsets.foreach(set => uniqItems ++= set)
>       uniqItems.toIterator.map((_, 1L))
>     }.reduceByKey(_ + _).filter { case (_, count) =>
>       count >= minCount
>     }.sortBy(-_._2).map(_._1).collect()
>   }
> {code}
> This issue is reported by our tool CacheCheck, which is used to dynamically detecting persist()/unpersist() api misuses.



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