[GitHub] spark pull request #16696: [SPARK-19350] [SQL] Cardinality estimation of Lim...

[ron8hu <gi...@git.apache.org>]

Github user ron8hu commented on a diff in the pull request:

    https://github.com/apache/spark/pull/16696#discussion_r99474494
  
    --- Diff: sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/statsEstimation/StatsEstimationSuite.scala ---
    @@ -18,12 +18,41 @@
     package org.apache.spark.sql.catalyst.statsEstimation
     
     import org.apache.spark.sql.catalyst.CatalystConf
    -import org.apache.spark.sql.catalyst.expressions.{Attribute, AttributeMap, AttributeReference}
    -import org.apache.spark.sql.catalyst.plans.logical.{ColumnStat, LogicalPlan, Statistics}
    +import org.apache.spark.sql.catalyst.expressions.{Attribute, AttributeMap, AttributeReference, Literal}
    +import org.apache.spark.sql.catalyst.plans.logical._
     import org.apache.spark.sql.types.IntegerType
     
     
    -class StatsConfSuite extends StatsEstimationTestBase {
    +class StatsEstimationSuite extends StatsEstimationTestBase {
    +  val (ar, colStat) = (attr("key"), ColumnStat(distinctCount = 10, min = Some(1), max = Some(10),
    +    nullCount = 0, avgLen = 4, maxLen = 4))
    +
    +  val plan = StatsTestPlan(
    +    outputList = Seq(ar),
    +    attributeStats = AttributeMap(Seq(ar -> colStat)),
    +    rowCount = 10,
    +    size = Some(10 * (8 + 4)))
    +
    +  test("limit estimation") {
    +    val localLimit = LocalLimit(Literal(2), plan)
    +    val globalLimit = GlobalLimit(Literal(2), plan)
    +    // LocalLimit and GlobalLimit share the same stats estimation logic.
    +    val expected = Statistics(sizeInBytes = 24, rowCount = Some(2))
    +    checkStats(localLimit, expected)
    +    checkStats(globalLimit, expected)
    +  }
    +
    +  test("sample estimation") {
    +    val sample = Sample(0.0, 0.5, withReplacement = false, (math.random * 1000).toLong, plan)()
    +    checkStats(sample, expected = Statistics(sizeInBytes = 60, rowCount = Some(5)))
    +
    +    // Test if Sample's child doesn't have rowCount in stats
    +    val stats2 = Statistics(sizeInBytes = 120)
    --- End diff --
    
    For limit estimation test cases, we may add a test with limit number greater than a child node's row count.  This test can show if we properly select the smaller value between limit number child node's row count. 


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