srowen commented on a change in pull request #26454: [SPARK-29818][MLLIB]
Missing persist on RDD
URL: https://github.com/apache/spark/pull/26454#discussion_r344509790
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File path: mllib/src/main/scala/org/apache/spark/ml/tuning/CrossValidator.scala
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@@ -141,8 +141,10 @@ class CrossValidator @Since("1.2.0") (@Since("1.4.0")
override val uid: String)
Some(Array.fill($(numFolds))(Array.fill[Model[_]](epm.length)(null)))
} else None
+ val inputRDD = dataset.toDF.rdd
+ inputRDD.persist()
Review comment:
Persisting takes time and resources. If it's only used once, it is likely to
make things slower.
Even where it might be reused a few times, it may not be worth it; kind of
depends on what the usages are. By default, I would not persist something
unless there's a pretty clear argument for it, like a benchmark or obvious
reason it's slow (used in a loop, etc)
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