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[SPARK-27351][SQL] Wrong outputRows estimation after AggregateEstimation with only null value column #24286

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[SPARK-27351][SQL] Wrong outputRows estimation after AggregateEstimation with only null value column #24286

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3e91bbe
SPARK-27351 Wrong outputRows estimation after AggregateEstimation wit…
Apr 3, 2019
7c7685c
merge upstream/master
Apr 11, 2019
aa9859a
check null value count for only null value column
pengbo Apr 11, 2019
6a9d35f
refine code to make columnStat.distinctCount.get called only once
pengbo Apr 14, 2019
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12 changes: 10 additions & 2 deletions ...ala/org/apache/spark/sql/catalyst/plans/logical/statsEstimation/AggregateEstimation.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -39,8 +39,16 @@ object AggregateEstimation {
// Multiply distinct counts of group-by columns. This is an upper bound, which assumes
// the data contains all combinations of distinct values of group-by columns.
var outputRows: BigInt = agg.groupingExpressions.foldLeft(BigInt(1))(
(res, expr) => res *
childStats.attributeStats(expr.asInstanceOf[Attribute]).distinctCount.get)
(res, expr) => {
val columnStat = childStats.attributeStats(expr.asInstanceOf[Attribute])
val distinctCount = columnStat.distinctCount.get
val distinctValue: BigInt = if (distinctCount == 0 && columnStat.nullCount.get > 0) {
1
} else {
distinctCount
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@gatorsmile gatorsmile Apr 22, 2019

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If the nullCount is not empty, the value should be distinctCount + 1, right?

@pengbo @dongjoon-hyun

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@pengbo pengbo Apr 22, 2019

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Good point.
I will try and test it out. Another PR will be submitted if the problem exists.

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@dongjoon-hyun dongjoon-hyun Apr 22, 2019

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Oh, right. @gatorsmile . Originally, this PR aims to fix the case of column with only null value, but that's another case which we should fix. Thanks!

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@srowen srowen Apr 22, 2019

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Oh, I inferred that the distinct count already correctly counted a null as a distinct value. If not, yeah, then distinctCount doesn't matter; it should add 1 iff nullCount is > 0. Agree, if this is broader, can we get an additional test of that case too?

}
res * distinctValue
})

outputRows = if (agg.groupingExpressions.isEmpty) {
// If there's no group-by columns, the output is a single row containing values of aggregate
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12 changes: 11 additions & 1 deletion ...c/test/scala/org/apache/spark/sql/catalyst/statsEstimation/AggregateEstimationSuite.scala
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Expand Up @@ -38,7 +38,9 @@ class AggregateEstimationSuite extends StatsEstimationTestBase with PlanTest {
attr("key22") -> ColumnStat(distinctCount = Some(2), min = Some(10), max = Some(20),
nullCount = Some(0), avgLen = Some(4), maxLen = Some(4)),
attr("key31") -> ColumnStat(distinctCount = Some(0), min = None, max = None,
nullCount = Some(0), avgLen = Some(4), maxLen = Some(4))
nullCount = Some(0), avgLen = Some(4), maxLen = Some(4)),
attr("key32") -> ColumnStat(distinctCount = Some(0), min = None, max = None,
nullCount = Some(4), avgLen = Some(4), maxLen = Some(4))
))

private val nameToAttr: Map[String, Attribute] = columnInfo.map(kv => kv._1.name -> kv._1)
Expand Down Expand Up @@ -116,6 +118,14 @@ class AggregateEstimationSuite extends StatsEstimationTestBase with PlanTest {
expectedOutputRowCount = 0)
}

test("group-by column with only null value") {
checkAggStats(
tableColumns = Seq("key22", "key32"),
tableRowCount = 6,
groupByColumns = Seq("key22", "key32"),
expectedOutputRowCount = nameToColInfo("key22")._2.distinctCount.get)
}

test("non-cbo estimation") {
val attributes = Seq("key12").map(nameToAttr)
val child = StatsTestPlan(
Expand Down