ReplaceExceptWithFilter Logical Optimization Rule — Rewriting Except (DISTINCT) Operators

ReplaceExceptWithFilter is a Catalyst rule for transforming logical plans (i.e. Rule[LogicalPlan]).

When executed, ReplaceExceptWithFilter transforms an Except (distinct) logical operator to…FIXME

ReplaceExceptWithFilter is a part of the Replace Operators fixed-point rule batch of the base Catalyst Optimizer.

ReplaceExceptWithFilter can be turned off and on based on spark.sql.optimizer.replaceExceptWithFilter configuration property.

Demo: ReplaceExceptWithFilter

import org.apache.spark.sql.catalyst.dsl.expressions._
import org.apache.spark.sql.catalyst.dsl.plans._

// Using hacks to disable two Catalyst DSL implicits
implicit def symbolToColumn(ack: ThatWasABadIdea) = ack
implicit class StringToColumn(val sc: StringContext) {}

import org.apache.spark.sql.catalyst.plans.logical.LocalRelation
val t1 = LocalRelation('a.int, 'b.int)
val t2 = t1.where('a > 5)

val plan = t1.except(t2, isAll = false)

import org.apache.spark.sql.catalyst.optimizer.ReplaceExceptWithFilter
val optimizedPlan = ReplaceExceptWithFilter(plan)
scala> println(optimizedPlan.numberedTreeString)
00 'Distinct
01 +- 'Filter NOT coalesce(('a > 5), false)
02    +- LocalRelation <empty>, [a#12, b#13]

`isEligible` Internal Predicate

isEligible(
  left: LogicalPlan,
  right: LogicalPlan): Boolean

isEligible is positive (true) when the right logical operator is a Project with a Filter child operator or simply a Filter operator itself and verifyConditions.

Otherwise, isEligible is negative (false).

Note	`isEligible` is used when `ReplaceExceptWithFilter` is executed.

`verifyConditions` Internal Predicate

verifyConditions(
  left: LogicalPlan,
  right: LogicalPlan): Boolean

verifyConditions is positive (true) when all of the following hold:

FIXME

Otherwise, verifyConditions is negative (false).

Note	`verifyConditions` is used when `ReplaceExceptWithFilter` is executed (when requested to isEligible).

ReplaceExceptWithFilter