[jira] [Created] (SPARK-32758) Spark ignores limit(1) and starts tasks for all partition

["Ivan Tsukanov (Jira)" <ji...@apache.org>]

Ivan Tsukanov created SPARK-32758:
-------------------------------------

             Summary: Spark ignores limit(1) and starts tasks for all partition
                 Key: SPARK-32758
                 URL: https://issues.apache.org/jira/browse/SPARK-32758
             Project: Spark
          Issue Type: Bug
          Components: Spark Core
    Affects Versions: 2.4.0
         Environment:  
 
должен
 
            Reporter: Ivan Tsukanov


If we run the following code
{code:scala}
  val sparkConf = new SparkConf()
    .setAppName("test-app")
    .setMaster("local[1]")
  val sparkSession = SparkSession.builder().config(sparkConf).getOrCreate()

  import sparkSession.implicits._

  val df = (1 to 100000)
    .toDF("c1")
    .repartition(1000)

  implicit val encoder: ExpressionEncoder[Row] = RowEncoder(df.schema)

  df.limit(1)
    .map(identity)
    .collect()

  df.map(identity)
    .limit(1)
    .collect()

  Thread.sleep(100000)
{code}
we will see that spark started 1002 tasks despite the fact there is limit(1) -

!image-2020-09-01-10-34-47-580.png!  

Expected behavior - both scenarios (limit before and after map) will produce the same results - one or two tasks to get one value from the DataFrame.



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