cloud-fan commented on a change in pull request #20965: [WIP][SPARK-21870][SQL]
Split aggregation code into small functions
URL: https://github.com/apache/spark/pull/20965#discussion_r318921802
##########
File path:
sql/core/src/main/scala/org/apache/spark/sql/execution/aggregate/HashAggregateExec.scala
##########
@@ -255,41 +260,138 @@ case class HashAggregateExec(
""".stripMargin
}
+ // Splits aggregate code into small functions because the most of JVM
implementations
+ // can not compile too long functions.
+ //
+ // Note: The difference from `CodeGenerator.splitExpressions` is that we
define an individual
+ // function for each aggregation function (e.g., SUM and AVG). For example,
in a query
+ // `SELECT SUM(a), AVG(a) FROM VALUES(1) t(a)`, we define two functions
+ // for `SUM(a)` and `AVG(a)`.
+ private def splitAggregateExpressions(
+ ctx: CodegenContext,
+ aggNames: Seq[String],
+ aggBufferUpdatingExprs: Seq[Seq[Expression]],
+ aggCodeBlocks: Seq[Block],
+ subExprs: Map[Expression, SubExprEliminationState]): Option[String] = {
+ val inputVars = aggBufferUpdatingExprs.map { aggExprsForOneFunc =>
+ val inputVarsForOneFunc = aggExprsForOneFunc.map(
+ CodeGenerator.getLocalInputVariableValues(ctx, _, subExprs)).reduce(_
++ _).toSeq
+ val paramLength =
CodeGenerator.calculateParamLengthFromExprValues(inputVarsForOneFunc)
+
+ // Checks if a parameter length for the `aggExprsForOneFunc` does not go
over the JVM limit
+ if (CodeGenerator.isValidParamLength(paramLength)) {
+ Some(inputVarsForOneFunc)
+ } else {
+ None
+ }
+ }
+
+ // Checks if all the aggregate code can be split into pieces.
+ // If the parameter length of at lease one `aggExprsForOneFunc` goes over
the limit,
+ // we totally give up splitting aggregate code.
+ if (inputVars.forall(_.isDefined)) {
+ val splitCodes = inputVars.flatten.zipWithIndex.map { case (args, i) =>
+ val doAggVal = ctx.freshName(s"doAggregateVal_${aggNames(i)}")
+ val argList = args.map(v => s"${v.javaType.getName}
${v.variableName}").mkString(", ")
+ val doAggValFuncName = ctx.addNewFunction(doAggVal,
+ s"""
+ |private void $doAggVal($argList) throws java.io.IOException {
+ | ${aggCodeBlocks(i)}
+ |}
+ """.stripMargin)
+
+ val inputVariables = args.map(_.variableName).mkString(", ")
+ s"$doAggValFuncName($inputVariables);"
+ }
+ Some(splitCodes.mkString("\n").trim)
+ } else {
+ val errMsg = "Failed to split aggregate code into small functions
because the parameter " +
+ "length of at least one split function went over the JVM limit: " +
+ CodeGenerator.MAX_JVM_METHOD_PARAMS_LENGTH
+ if (Utils.isTesting) {
+ throw new IllegalStateException(errMsg)
+ } else {
+ logInfo(errMsg)
+ None
+ }
+ }
+ }
+
private def doConsumeWithoutKeys(ctx: CodegenContext, input: Seq[ExprCode]):
String = {
// only have DeclarativeAggregate
val functions =
aggregateExpressions.map(_.aggregateFunction.asInstanceOf[DeclarativeAggregate])
val inputAttrs = functions.flatMap(_.aggBufferAttributes) ++ child.output
- val updateExpr = aggregateExpressions.flatMap { e =>
+ // To individually generate code for each aggregate function, an element
in `updateExprs` holds
+ // all the expressions for the buffer of an aggregation function.
+ val updateExprs = aggregateExpressions.map { e =>
e.mode match {
case Partial | Complete =>
e.aggregateFunction.asInstanceOf[DeclarativeAggregate].updateExpressions
case PartialMerge | Final =>
e.aggregateFunction.asInstanceOf[DeclarativeAggregate].mergeExpressions
}
}
- ctx.currentVars = bufVars ++ input
- val boundUpdateExpr = bindReferences(updateExpr, inputAttrs)
- val subExprs =
ctx.subexpressionEliminationForWholeStageCodegen(boundUpdateExpr)
+ ctx.currentVars = bufVars.flatten ++ input
+ val boundUpdateExprs = updateExprs.map { updateExprsForOneFunc =>
+ bindReferences(updateExprsForOneFunc, inputAttrs)
+ }
+ val subExprs =
ctx.subexpressionEliminationForWholeStageCodegen(boundUpdateExprs.flatten)
val effectiveCodes = subExprs.codes.mkString("\n")
Review comment:
BTW the variables are badly named in this file...
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