Github user cloud-fan commented on a diff in the pull request:

    https://github.com/apache/spark/pull/16430#discussion_r95098331
  
    --- Diff: 
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/statsEstimation/ProjectEstimation.scala
 ---
    @@ -0,0 +1,44 @@
    +/*
    + * 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.plans.logical.statsEstimation
    +
    +import org.apache.spark.sql.catalyst.expressions.{Alias, Attribute, 
AttributeMap}
    +import org.apache.spark.sql.catalyst.plans.logical.{Project, Statistics}
    +
    +object ProjectEstimation {
    +  import EstimationUtils._
    +
    +  def estimate(project: Project): Option[Statistics] = {
    +    if (rowCountsExist(project.child)) {
    +      val childStats = project.child.statistics
    +      val inputAttrStats = childStats.attributeStats
    +      // Match alias with its child's column stat
    +      val aliasStats = project.expressions.collect {
    +        case alias @ Alias(attr: Attribute, _) if 
inputAttrStats.contains(attr) =>
    --- End diff --
    
    In the long run, we should define a `statistics` interface in `Expression`, 
so that we can propagate the column stats more naturally, for more cases(not 
only `Alias`, but also `Add`, `Mod`, etc.). But currently catalyst doesn't 
propagate attributes correctly, e.g. 
https://issues.apache.org/jira/browse/SPARK-17995 (`Union`, `Except`, etc. has 
the same problem), we may need to hack a lot of places to propagate column 
stats correctly.
    
    According to @wzhfy 's benchmark, it turns out we can speed up most of the 
cases if we take care of `Alias`, so I'm ok with the current approach.


---
If your project is set up for it, you can reply to this email and have your
reply appear on GitHub as well. If your project does not have this feature
enabled and wishes so, or if the feature is enabled but not working, please
contact infrastructure at infrastruct...@apache.org or file a JIRA ticket
with INFRA.
---

---------------------------------------------------------------------
To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org
For additional commands, e-mail: reviews-h...@spark.apache.org

Reply via email to