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[VL] Compatible lag function in spark-3.0 #7168

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[VL] Compatible lag function in spark-3.0 #7168

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5426936
fix window function lag typo error
kecookier Sep 9, 2024
171b7a4
add ut
kecookier Sep 9, 2024
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14 changes: 13 additions & 1 deletion backends-velox/src/test/scala/org/apache/gluten/execution/WindowFunctionsValidateSuite.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -19,14 +19,26 @@ package org.apache.gluten.execution
class WindowFunctionsValidateSuite extends FunctionsValidateSuite {

test("lag/lead window function with negative input offset") {
runQueryAndCompare(
"select l_suppkey,lag(l_orderkey, -2) over" +
" (partition by l_suppkey order by l_orderkey) from lineitem") {
checkGlutenOperatorMatch[WindowExecTransformer]
}

runQueryAndCompare(
"select l_suppkey, lead(l_orderkey, -2) over" +
" (partition by l_suppkey order by l_orderkey) from lineitem") {
checkGlutenOperatorMatch[WindowExecTransformer]
}

runQueryAndCompare(
"select lag(l_orderkey, -2) over" +
" (partition by l_suppkey order by l_orderkey) from lineitem") {
checkGlutenOperatorMatch[WindowExecTransformer]
}

runQueryAndCompare(
"select lead(l_orderkey, -2) over" +
"select lag(l_orderkey, 2) over" +
" (partition by l_suppkey order by l_orderkey) from lineitem") {
checkGlutenOperatorMatch[WindowExecTransformer]
}
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2 changes: 1 addition & 1 deletion gluten-substrait/src/main/scala/org/apache/gluten/expression/WindowFunctionsBuilder.scala
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Expand Up @@ -31,7 +31,7 @@ object WindowFunctionsBuilder {
val substraitFunc = windowFunc match {
// Handle lag with negative inputOffset, e.g., converts lag(c1, -1) to lead(c1, 1).
// Spark uses `-inputOffset` as `offset` for Lag function.
case lag: Lag if lag.offset.eval(EmptyRow).asInstanceOf[Int] > 0 =>
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@kecookier, seems offset > 0 implies inputOffset < 0, so the original handling is expected, right?

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@PHILO-HE This PR addresses the lag result mismatch issue in my current version of Spark. Thank you for your input. I have reviewed the Spark code, and now I understand the differences.

In Spark 3.0, the LAG function calculates the bound using both the offset and the direction. However, in versions post Spark 3.1, the function does not consider the direction. Instead, it uses a single literal expression that includes the offset of the current row to calculate the bound. For example, in lag(), the offset will be wrapped with UnaryMinus(offset).

lag in spark 3.0 https://github.com/apache/spark/blob/branch-3.0/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/windowExpressions.scala#L474

lag in spark 3.2 https://github.com/apache/spark/blob/branch-3.2/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/windowExpressions.scala#L538

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@kecookier, I see. Thanks for your clarification! Seems there is no way to let gluten adapt to the two implementations. Should you fix it in a forked gluten on your side?

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Ok, I will close this PR.

case lag: Lag if lag.offset.eval(EmptyRow).asInstanceOf[Int] < 0 =>
Some(LEAD)
// Handle lead with negative offset, e.g., converts lead(c1, -1) to lag(c1, 1).
case lead: Lead if lead.offset.eval(EmptyRow).asInstanceOf[Int] < 0 =>
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