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From cloud-fan <...@git.apache.org>
Subject [GitHub] spark pull request #19813: [SPARK-22600][SQL] Fix 64kb limit for deeply nest...
Date Mon, 11 Dec 2017 14:25:02 GMT
Github user cloud-fan commented on a diff in the pull request:

    https://github.com/apache/spark/pull/19813#discussion_r156086133
  
    --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/codegen/ExpressionCodegen.scala
---
    @@ -0,0 +1,246 @@
    +/*
    + * Licensed to the Apache Software Foundation (ASF) under one or more
    + * contributor license agreements.  See the NOTICE file distributed with
    + * this work for additional information regarding copyright ownership.
    + * The ASF licenses this file to You 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 org.apache.spark.sql.catalyst.expressions.codegen
    +
    +import scala.collection.mutable
    +
    +import org.apache.spark.sql.catalyst.expressions._
    +import org.apache.spark.sql.types.DataType
    +
    +/**
    + * Defines util methods used in expression code generation.
    + */
    +object ExpressionCodegen {
    +
    +  // Type alias for a tuple representing the data type and nullable for an expression.
    +  type ExprProperty = (DataType, Boolean)
    +
    +  /**
    +   * Given an expression, returns the all necessary parameters to evaluate it, so the
generated
    +   * code of this expression can be split in a function.
    +   * The 1st string in returned tuple is the parameter strings used to call the function.
    +   * The 2nd string in returned tuple is the parameter strings used to declare the function.
    +   *
    +   * Returns `None` if it can't produce valid parameters.
    +   *
    +   * Params to include:
    +   * 1. Evaluated columns referred by this, children or deferred expressions.
    +   * 2. Rows referred by this, children or deferred expressions.
    +   * 3. Eliminated subexpressions referred by children expressions.
    +   */
    +  def getExpressionInputParams(
    +      ctx: CodegenContext,
    +      expr: Expression): Option[(Seq[String], Seq[String])] = {
    +    val (inputAttrs, inputVars) = getInputVarsForChildren(ctx, expr)
    +    val paramsFromColumns = prepareFunctionParams(ctx, inputAttrs, inputVars)
    +
    +    val subExprs = getSubExprInChildren(ctx, expr)
    +    val subExprCodes = getSubExprCodes(ctx, subExprs)
    +    val subAttrs = subExprs.map(e => (e.dataType, e.nullable))
    +    val paramsFromSubExprs = prepareFunctionParams(ctx, subAttrs, subExprCodes)
    +
    +    val inputRows = ctx.INPUT_ROW +: getInputRowsForChildren(ctx, expr)
    +    val paramsFromRows = inputRows.distinct.filter(_ != null).map { row =>
    +      (row, s"InternalRow $row")
    +    }
    +
    +    val paramsLength = getParamLength(ctx, inputAttrs ++ subAttrs) + paramsFromRows.length
    +    // Maximum allowed parameter number for Java's method descriptor.
    +    if (paramsLength > 255) {
    +      None
    +    } else {
    +      val allParams = (paramsFromRows ++ paramsFromColumns ++ paramsFromSubExprs).unzip
    +      val callParams = allParams._1.distinct
    +      val declParams = allParams._2.distinct
    +      Some((callParams, declParams))
    +    }
    +  }
    +
    +  /**
    +   * Returns the eliminated subexpressions in the children expressions.
    +   */
    +  def getSubExprInChildren(ctx: CodegenContext, expr: Expression): Seq[Expression] =
{
    +    expr.children.flatMap { child =>
    +      child.collect {
    +        case e if ctx.subExprEliminationExprs.contains(e) => e
    +      }
    +    }.distinct
    +  }
    +
    +  /**
    +   * A small helper function to return `ExprCode`s that represent subexpressions.
    +   */
    +  def getSubExprCodes(ctx: CodegenContext, subExprs: Seq[Expression]): Seq[ExprCode]
= {
    --- End diff --
    
    in normal codegen the sub-expr `value` and `isNull` are all global variables.


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