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conditionalExpressions.scala
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conditionalExpressions.scala
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/*
* Copyright (c) 2020-2022, NVIDIA CORPORATION.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.nvidia.spark.rapids
import ai.rapids.cudf.{BinaryOp, ColumnVector, DType, NullPolicy, Scalar, ScanAggregation, ScanType, Table, UnaryOp}
import com.nvidia.spark.rapids.RapidsPluginImplicits._
import com.nvidia.spark.rapids.shims.v2.ShimExpression
import org.apache.spark.sql.catalyst.analysis.{TypeCheckResult, TypeCoercion}
import org.apache.spark.sql.catalyst.expressions.{ComplexTypeMergingExpression, Expression}
import org.apache.spark.sql.types.{BooleanType, DataType, DataTypes}
import org.apache.spark.sql.vectorized.ColumnarBatch
trait GpuConditionalExpression extends ComplexTypeMergingExpression with GpuExpression
with ShimExpression {
protected def computeIfElse(
batch: ColumnarBatch,
predExpr: Expression,
trueExpr: Expression,
falseValue: Any): GpuColumnVector = {
withResourceIfAllowed(falseValue) { falseRet =>
withResource(GpuExpressionsUtils.columnarEvalToColumn(predExpr, batch)) { pred =>
withResourceIfAllowed(trueExpr.columnarEval(batch)) { trueRet =>
val finalRet = (trueRet, falseRet) match {
case (t: GpuColumnVector, f: GpuColumnVector) =>
pred.getBase.ifElse(t.getBase, f.getBase)
case (t: GpuScalar, f: GpuColumnVector) =>
pred.getBase.ifElse(t.getBase, f.getBase)
case (t: GpuColumnVector, f: GpuScalar) =>
pred.getBase.ifElse(t.getBase, f.getBase)
case (t: GpuScalar, f: GpuScalar) =>
pred.getBase.ifElse(t.getBase, f.getBase)
case (t, f) =>
throw new IllegalStateException(s"Unexpected inputs" +
s" ($t: ${t.getClass}, $f: ${f.getClass})")
}
GpuColumnVector.from(finalRet, dataType)
}
}
}
}
protected def isAllTrue(col: GpuColumnVector): Boolean = {
assert(BooleanType == col.dataType())
if (col.getRowCount == 0) {
return true
}
if (col.hasNull) {
return false
}
withResource(col.getBase.all()) { allTrue =>
// Guaranteed there is at least one row and no nulls so result must be valid
allTrue.getBoolean
}
}
protected def isAllFalse(col: GpuColumnVector): Boolean = {
assert(BooleanType == col.dataType())
if (col.getRowCount == col.numNulls()) {
// all nulls, and null values are false values here
return true
}
withResource(col.getBase.any()) { anyTrue =>
// null values are considered false values in this context
!anyTrue.getBoolean
}
}
protected def filterBatch(
tbl: Table,
pred: ColumnVector,
colTypes: Array[DataType]): ColumnarBatch = {
withResource(tbl.filter(pred)) { filteredData =>
GpuColumnVector.from(filteredData, colTypes)
}
}
private def boolToInt(cv: ColumnVector): ColumnVector = {
withResource(GpuScalar.from(1, DataTypes.IntegerType)) { one =>
withResource(GpuScalar.from(0, DataTypes.IntegerType)) { zero =>
cv.ifElse(one, zero)
}
}
}
/**
* Invert boolean values and convert null values to true
*/
def boolInverted(cv: ColumnVector): ColumnVector = {
withResource(GpuScalar.from(true, DataTypes.BooleanType)) { t =>
withResource(GpuScalar.from(false, DataTypes.BooleanType)) { f =>
cv.ifElse(f, t)
}
}
}
protected def gather(predicate: ColumnVector, t: GpuColumnVector): ColumnVector = {
// convert the predicate boolean column to numeric where 1 = true
// and 0 (or null) = false and then use `scan` with `sum` to convert to
// indices.
//
// For example, if the predicate evaluates to [F, null, T, F, T] then this
// gets translated first to [0, 0, 1, 0, 1] and then the scan operation
// will perform an exclusive sum on these values and
// produce [0, 0, 0, 1, 1]. Combining this with the original
// predicate boolean array results in the two T values mapping to
// indices 0 and 1, respectively.
val prefixSumExclusive = withResource(boolToInt(predicate)) { boolsAsInts =>
boolsAsInts.scan(
ScanAggregation.sum(),
ScanType.EXCLUSIVE,
NullPolicy.INCLUDE)
}
val gatherMap = withResource(prefixSumExclusive) { prefixSumExclusive =>
// for the entries in the gather map that do not represent valid
// values to be gathered, we change the value to -MAX_INT which
// will be treated as null values in the gather algorithm
withResource(Scalar.fromInt(Int.MinValue)) {
outOfBoundsFlag => predicate.ifElse(prefixSumExclusive, outOfBoundsFlag)
}
}
withResource(gatherMap) { _ =>
withResource(new Table(t.getBase)) { tbl =>
withResource(tbl.gather(gatherMap)) { gatherTbl =>
gatherTbl.getColumn(0).incRefCount()
}
}
}
}
}
case class GpuIf(
predicateExpr: Expression,
trueExpr: Expression,
falseExpr: Expression) extends GpuConditionalExpression {
@transient
override lazy val inputTypesForMerging: Seq[DataType] = {
Seq(trueExpr.dataType, falseExpr.dataType)
}
override def children: Seq[Expression] = predicateExpr :: trueExpr :: falseExpr :: Nil
override def nullable: Boolean = trueExpr.nullable || falseExpr.nullable
override def checkInputDataTypes(): TypeCheckResult = {
if (predicateExpr.dataType != BooleanType) {
TypeCheckResult.TypeCheckFailure(
"type of predicate expression in If should be boolean, " +
s"not ${predicateExpr.dataType.catalogString}")
} else if (!TypeCoercion.haveSameType(inputTypesForMerging)) {
TypeCheckResult.TypeCheckFailure(s"differing types in '$sql' " +
s"(${trueExpr.dataType.catalogString} and ${falseExpr.dataType.catalogString}).")
} else {
TypeCheckResult.TypeCheckSuccess
}
}
override def columnarEval(batch: ColumnarBatch): Any = {
val gpuTrueExpr = trueExpr.asInstanceOf[GpuExpression]
val gpuFalseExpr = falseExpr.asInstanceOf[GpuExpression]
withResource(GpuExpressionsUtils.columnarEvalToColumn(predicateExpr, batch)) { pred =>
if (isAllTrue(pred)) {
GpuExpressionsUtils.columnarEvalToColumn(trueExpr, batch)
} else if (isAllFalse(pred)) {
GpuExpressionsUtils.columnarEvalToColumn(falseExpr, batch)
} else if (gpuTrueExpr.hasSideEffects || gpuFalseExpr.hasSideEffects) {
conditionalWithSideEffects(batch, pred, gpuTrueExpr, gpuFalseExpr)
} else {
withResourceIfAllowed(trueExpr.columnarEval(batch)) { trueRet =>
withResourceIfAllowed(falseExpr.columnarEval(batch)) { falseRet =>
val finalRet = (trueRet, falseRet) match {
case (t: GpuColumnVector, f: GpuColumnVector) =>
pred.getBase.ifElse(t.getBase, f.getBase)
case (t: GpuScalar, f: GpuColumnVector) =>
pred.getBase.ifElse(t.getBase, f.getBase)
case (t: GpuColumnVector, f: GpuScalar) =>
pred.getBase.ifElse(t.getBase, f.getBase)
case (t: GpuScalar, f: GpuScalar) =>
pred.getBase.ifElse(t.getBase, f.getBase)
case (t, f) =>
throw new IllegalStateException(s"Unexpected inputs" +
s" ($t: ${t.getClass}, $f: ${f.getClass})")
}
GpuColumnVector.from(finalRet, dataType)
}
}
}
}
}
/**
* When computing conditional expressions on the CPU, the true and false
* expressions are evaluated lazily, meaning that the true expression is
* only evaluated for rows where the predicate is true, and the false
* expression is only evaluated for rows where the predicate is false.
* This is important in the case where the expressions can have
* side-effects, such as throwing exceptions for invalid inputs.
*
* This method performs lazy evaluation on the GPU by first filtering the
* input batch into two batches - one for rows where the predicate is true
* and one for rows where the predicate is false. The expressions are
* evaluated against these batches and then the results are combined
* back into a single batch using the gather algorithm.
*/
private def conditionalWithSideEffects(
batch: ColumnarBatch,
pred: GpuColumnVector,
gpuTrueExpr: GpuExpression,
gpuFalseExpr: GpuExpression): GpuColumnVector = {
val colTypes = GpuColumnVector.extractTypes(batch)
withResource(GpuColumnVector.from(batch)) { tbl =>
withResource(pred.getBase.unaryOp(UnaryOp.NOT)) { inverted =>
// evaluate true expression against true batch
val tt = withResource(filterBatch(tbl, pred.getBase, colTypes)) { trueBatch =>
gpuTrueExpr.columnarEval(trueBatch)
}
withResourceIfAllowed(tt) { _ =>
// evaluate false expression against false batch
val ff = withResource(filterBatch(tbl, inverted, colTypes)) { falseBatch =>
gpuFalseExpr.columnarEval(falseBatch)
}
withResourceIfAllowed(ff) { _ =>
val finalRet = (tt, ff) match {
case (t: GpuColumnVector, f: GpuColumnVector) =>
withResource(gather(pred.getBase, t)) { trueValues =>
withResource(gather(inverted, f)) { falseValues =>
pred.getBase.ifElse(trueValues, falseValues)
}
}
case (t: GpuScalar, f: GpuColumnVector) =>
withResource(gather(inverted, f)) { falseValues =>
pred.getBase.ifElse(t.getBase, falseValues)
}
case (t: GpuColumnVector, f: GpuScalar) =>
withResource(gather(pred.getBase, t)) { trueValues =>
pred.getBase.ifElse(trueValues, f.getBase)
}
case (_: GpuScalar, _: GpuScalar) =>
throw new IllegalStateException(
"scalar expressions can never have side effects")
}
GpuColumnVector.from(finalRet, dataType)
}
}
}
}
}
override def toString: String = s"if ($predicateExpr) $trueExpr else $falseExpr"
override def sql: String = s"(IF(${predicateExpr.sql}, ${trueExpr.sql}, ${falseExpr.sql}))"
}
case class GpuCaseWhen(
branches: Seq[(Expression, Expression)],
elseValue: Option[Expression] = None) extends GpuConditionalExpression with Serializable {
override def children: Seq[Expression] = branches.flatMap(b => b._1 :: b._2 :: Nil) ++ elseValue
// both then and else expressions should be considered.
@transient
override lazy val inputTypesForMerging: Seq[DataType] = {
branches.map(_._2.dataType) ++ elseValue.map(_.dataType)
}
private lazy val branchesWithSideEffects =
branches.exists(_._2.asInstanceOf[GpuExpression].hasSideEffects)
override def nullable: Boolean = {
// Result is nullable if any of the branch is nullable, or if the else value is nullable
branches.exists(_._2.nullable) || elseValue.forall(_.nullable)
}
override def checkInputDataTypes(): TypeCheckResult = {
if (TypeCoercion.haveSameType(inputTypesForMerging)) {
// Make sure all branch conditions are boolean types.
if (branches.forall(_._1.dataType == BooleanType)) {
TypeCheckResult.TypeCheckSuccess
} else {
val index = branches.indexWhere(_._1.dataType != BooleanType)
TypeCheckResult.TypeCheckFailure(
s"WHEN expressions in CaseWhen should all be boolean type, " +
s"but the ${index + 1}th when expression's type is ${branches(index)._1}")
}
} else {
val branchesStr = branches.map(_._2.dataType).map(dt => s"WHEN ... THEN ${dt.catalogString}")
.mkString(" ")
val elseStr = elseValue.map(expr => s" ELSE ${expr.dataType.catalogString}").getOrElse("")
TypeCheckResult.TypeCheckFailure(
"THEN and ELSE expressions should all be same type or coercible to a common type," +
s" got CASE $branchesStr$elseStr END")
}
}
override def columnarEval(batch: ColumnarBatch): Any = {
if (branchesWithSideEffects) {
columnarEvalWithSideEffects(batch)
} else {
// `elseRet` will be closed in `computeIfElse`.
val elseRet = elseValue
.map(_.columnarEval(batch))
.getOrElse(GpuScalar(null, branches.last._2.dataType))
branches.foldRight[Any](elseRet) {
case ((predicateExpr, trueExpr), falseRet) =>
computeIfElse(batch, predicateExpr, trueExpr, falseRet)
}
}
}
/**
* Perform lazy evaluation of each branch so that we only evaluate the THEN expressions
* against rows where the WHEN expression is true.
*/
private def columnarEvalWithSideEffects(batch: ColumnarBatch): Any = {
val colTypes = GpuColumnVector.extractTypes(batch)
// track cumulative state of predicate evaluation per row so that we never evaluate expressions
// for a row if an earlier expression has already been evaluated to true for that row
var cumulativePred: Option[GpuColumnVector] = None
// this variable contains the currently evaluated value for each row and gets updated
// as each branch is evaluated
var currentValue: Option[GpuColumnVector] = None
try {
withResource(GpuColumnVector.from(batch)) { tbl =>
// iterate over the WHEN THEN branches first
branches.foreach {
case (whenExpr, thenExpr) =>
// evaluate the WHEN predicate
withResource(GpuExpressionsUtils.columnarEvalToColumn(whenExpr, batch)) { whenBool =>
// we only want to evaluate where this WHEN is true and no previous WHEN has been true
val firstTrueWhen = isFirstTrueWhen(cumulativePred, whenBool)
withResource(firstTrueWhen) { _ =>
if (isAllTrue(firstTrueWhen)) {
// if this WHEN predicate is true for all rows and no previous predicate has
// been true then we can return immediately
return GpuExpressionsUtils.columnarEvalToColumn(thenExpr, batch)
}
val thenValues = filterEvaluateWhenThen(colTypes, tbl, firstTrueWhen.getBase,
thenExpr)
withResource(thenValues) { _ =>
currentValue = Some(calcCurrentValue(currentValue, firstTrueWhen, thenValues))
}
cumulativePred = Some(calcCumulativePredicate(
cumulativePred, whenBool, firstTrueWhen))
if (isAllTrue(cumulativePred.get)) {
// no need to process any more branches or the else condition
return currentValue.get.incRefCount()
}
}
}
}
// invert the cumulative predicate to get the ELSE predicate
withResource(boolInverted(cumulativePred.get.getBase)) { elsePredNoNulls =>
elseValue match {
case Some(expr) =>
if (isAllFalse(cumulativePred.get)) {
GpuExpressionsUtils.columnarEvalToColumn(expr, batch)
} else {
val elseValues = filterEvaluateWhenThen(colTypes, tbl, elsePredNoNulls, expr)
withResource(elseValues) { _ =>
GpuColumnVector.from(elsePredNoNulls.ifElse(
elseValues, currentValue.get.getBase), dataType)
}
}
case None =>
// if there is no ELSE condition then we return NULL for any rows not matched by
// previous branches
withResource(GpuScalar.from(null, dataType)) { nullScalar =>
if (isAllFalse(cumulativePred.get)) {
GpuColumnVector.from(nullScalar, elsePredNoNulls.getRowCount.toInt, dataType)
} else {
GpuColumnVector.from(
elsePredNoNulls.ifElse(nullScalar, currentValue.get.getBase),
dataType)
}
}
}
}
}
} finally {
currentValue.foreach(_.safeClose())
cumulativePred.foreach(_.safeClose())
}
}
/**
* Filter the batch to just the rows where the WHEN condition is true and
* then evaluate the THEN expression.
*/
private def filterEvaluateWhenThen(
colTypes: Array[DataType],
tbl: Table,
whenBool: ColumnVector,
thenExpr: Expression): ColumnVector = {
val filteredBatch = filterBatch(tbl, whenBool, colTypes)
val thenValues = withResource(filteredBatch) { trueBatch =>
GpuExpressionsUtils.columnarEvalToColumn(thenExpr, trueBatch)
}
withResource(thenValues) { _ =>
gather(whenBool, thenValues)
}
}
/**
* Calculate the cumulative predicate so far using the logical expression
* `prevPredicate OR thisPredicate`.
*/
private def calcCumulativePredicate(
cumulativePred: Option[GpuColumnVector],
whenBool: GpuColumnVector,
firstTrueWhen: GpuColumnVector): GpuColumnVector = {
cumulativePred match {
case Some(prev) =>
withResource(prev) { _ =>
val result = prev.getBase.binaryOp(BinaryOp.NULL_LOGICAL_OR,
whenBool.getBase, DType.BOOL8)
GpuColumnVector.from(result, DataTypes.BooleanType)
}
case _ =>
firstTrueWhen.incRefCount()
}
}
/**
* Calculate the current values by merging the THEN values for this branch (where the WHEN
* predicate was true) with the previous values.
*/
private def calcCurrentValue(
prevValue: Option[GpuColumnVector],
whenBool: GpuColumnVector,
thenValues: ColumnVector): GpuColumnVector = {
prevValue match {
case Some(v) =>
withResource(v) { _ =>
GpuColumnVector.from(whenBool.getBase.ifElse(thenValues, v.getBase), dataType)
}
case _ =>
GpuColumnVector.from(thenValues.incRefCount(), dataType)
}
}
/**
* Determine for each row whether this is the first WHEN predicate so far to evaluate to true
*/
private def isFirstTrueWhen(
cumulativePred: Option[GpuColumnVector],
whenBool: GpuColumnVector): GpuColumnVector = {
cumulativePred match {
case Some(prev) =>
withResource(boolInverted(prev.getBase)) { notPrev =>
val whenReplaced = withResource(Scalar.fromBool(false)) { falseScalar =>
whenBool.getBase.replaceNulls(falseScalar)
}
withResource(whenReplaced) { _ =>
GpuColumnVector.from(whenReplaced.and(notPrev), DataTypes.BooleanType)
}
}
case None =>
whenBool.incRefCount()
}
}
override def toString: String = {
val cases = branches.map { case (c, v) => s" WHEN $c THEN $v" }.mkString
val elseCase = elseValue.map(" ELSE " + _).getOrElse("")
"CASE" + cases + elseCase + " END"
}
override def sql: String = {
val cases = branches.map { case (c, v) => s" WHEN ${c.sql} THEN ${v.sql}" }.mkString
val elseCase = elseValue.map(" ELSE " + _.sql).getOrElse("")
"CASE" + cases + elseCase + " END"
}
}