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From: davies <git@git.apache.org>
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Subject: [GitHub] spark pull request: [SPARK-14275][SQL] Reimplement
 TypedAggregateE...
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Message-Id: <20160413201657.903EADFC4F@git1-us-west.apache.org>
Date: Wed, 13 Apr 2016 20:16:57 +0000 (UTC)

Github user davies commented on a diff in the pull request:

    https://github.com/apache/spark/pull/12067#discussion_r59617422
  
    --- Diff: sql/core/src/main/scala/org/apache/spark/sql/execution/aggregate/TypedAggregateExpression.scala ---
    @@ -19,133 +19,153 @@ package org.apache.spark.sql.execution.aggregate
     
     import scala.language.existentials
     
    -import org.apache.spark.internal.Logging
     import org.apache.spark.sql.Encoder
    -import org.apache.spark.sql.catalyst.InternalRow
    -import org.apache.spark.sql.catalyst.encoders.{encoderFor, ExpressionEncoder, OuterScopes}
    +import org.apache.spark.sql.catalyst.analysis.{UnresolvedAttribute, UnresolvedDeserializer, UnresolvedExtractValue}
    +import org.apache.spark.sql.catalyst.encoders.encoderFor
     import org.apache.spark.sql.catalyst.expressions._
    -import org.apache.spark.sql.catalyst.expressions.aggregate.ImperativeAggregate
    +import org.apache.spark.sql.catalyst.expressions.aggregate.DeclarativeAggregate
     import org.apache.spark.sql.expressions.Aggregator
     import org.apache.spark.sql.types._
     
     object TypedAggregateExpression {
    -  def apply[A, B : Encoder, C : Encoder](
    -      aggregator: Aggregator[A, B, C]): TypedAggregateExpression = {
    +  def apply[BUF : Encoder, OUT : Encoder](
    +      aggregator: Aggregator[_, BUF, OUT]): TypedAggregateExpression = {
    +    val bufferEncoder = encoderFor[BUF]
    +    // We will insert the deserializer and function call expression at the bottom of each serializer
    +    // expression while executing `TypedAggregateExpression`, which means multiply serializer
    +    // expressions will all evaluate the same sub-expression at bottom.  To avoid the re-evaluating,
    +    // here we always use one single serializer expression to serialize the buffer object into a
    +    // single-field row, no matter whether the encoder is flat or not.  We also need to update the
    +    // deserializer to read in all fields from that single-field row.
    +    // TODO: remove this trick after we have  better integration of subexpression elimination and
    --- End diff --
    
    Can we hold this pr a little bit? let me think of how to do subexpression elimination in aggregate.


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