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https://issues.apache.org/jira/browse/SPARK-26534?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16735214#comment-16735214
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Liang-Chi Hsieh commented on SPARK-26534:
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I think the only difference is using Dataset or RDD. Can you replace with RDD
and see if the issue is still?
> Closure Cleaner Bug
> -------------------
>
> Key: SPARK-26534
> URL: https://issues.apache.org/jira/browse/SPARK-26534
> Project: Spark
> Issue Type: Bug
> Components: Spark Core
> Affects Versions: 2.3.1
> Reporter: sam
> Priority: Major
>
> I've found a strange combination of closures where the closure cleaner
> doesn't seem to be smart enough to figure out how to remove a reference that
> is not used. I.e. we get a `org.apache.spark.SparkException: Task not
> serializable` for a Task that is perfectly serializable.
>
> In the example below, the only `val` that is actually needed for the closure
> of the `map` is `foo`, but it tries to serialise `thingy`. What is odd is
> changing this code in a number of subtle ways eliminates the error, which
> I've tried to highlight using comments inline.
>
> {code:java}
> import org.apache.spark.sql._
> object Test {
> val sparkSession: SparkSession =
> SparkSession.builder.master("local").appName("app").getOrCreate()
> def apply(): Unit = {
> import sparkSession.implicits._
> val landedData: Dataset[String] =
> sparkSession.sparkContext.makeRDD(Seq("foo", "bar")).toDS()
> // thingy has to be in this outer scope to reproduce, if in someFunc,
> cannot reproduce
> val thingy: Thingy = new Thingy
> // If not wrapped in someFunc cannot reproduce
> val someFunc = () => {
> // If don't reference this foo inside the closer (e.g. just use
> identity function) cannot reproduce
> val foo: String = "foo"
> thingy.run(block = () => {
> landedData.map(r => {
> r + foo
> })
> .count()
> })
> }
> someFunc()
> }
> }
> class Thingy {
> def run[R](block: () => R): R = {
> block()
> }
> }
> {code}
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