Class RemoveSubPlansWithEmptyResults

java.lang.Object

se.liu.ida.hefquin.engine.queryproc.impl.loptimizer.heuristics.RemoveSubPlansWithEmptyResults

All Implemented Interfaces:

HeuristicForLogicalOptimization

public class RemoveSubPlansWithEmptyResults
extends Object
implements HeuristicForLogicalOptimization

Removes every subplan that is guaranteed to produce an empty result according to the cardinality estimate that is determined for it. In particular, a subplan is removed if it has a cardinality estimate of 0 with the quality score being QueryPlanProperty.Quality.ACCURATE. The subplans are removed in a top-down manner (i.e., trying to remove bigger subplans first).

The heuristic performs a recursive traversal of the logical plan and simplifies the plan based on emptiness information:

• If the overall plan itself is provably empty, it is replaced by LogicalPlanWithoutResult.
• For union and multiway union operators, empty subplans are removed. If exactly one subplan remains, the union operator is removed and replaced by that subplan.
• For left join operators, if the right subplan is empty, the left join is removed and replaced by its left subplan.
• For all other operators, empty subplans are not removed individually. Instead, emptiness is propagated via cardinality estimates, allowing higher-level simplifications when possible.

The heuristic relies on precomputed cardinality estimates provided by the CardinalityEstimator.

Field Summary

Fields

Modifier and Type	Field	Description
protected final CardinalityEstimator	cardEst

Constructor Summary

Constructors

Constructor	Description
RemoveSubPlansWithEmptyResults(CardinalityEstimator cardEst)
RemoveSubPlansWithEmptyResults(QueryProcContext ctxt)

Method Summary

Modifier and Type	Method	Description
protected LogicalPlan	_apply(LogicalPlan inputPlan)
LogicalPlan	apply(LogicalPlan inputPlan)	Applies this heuristics to the given plan and returns the resulting, potentially rewritten plan.
protected boolean	isProvablyEmpty(LogicalPlan plan)	Returns true if, according to the cardinality estimate that has been determined for the given plan, the plan is guaranteed to produce an empty result.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

cardEst

protected final CardinalityEstimator cardEst

Constructor Details

RemoveSubPlansWithEmptyResults

public RemoveSubPlansWithEmptyResults(QueryProcContext ctxt)

RemoveSubPlansWithEmptyResults

public RemoveSubPlansWithEmptyResults(CardinalityEstimator cardEst)

Method Details

apply

public LogicalPlan apply(LogicalPlan inputPlan)

Description copied from interface: HeuristicForLogicalOptimization

Applies this heuristics to the given plan and returns the resulting, potentially rewritten plan.

Specified by:

apply in interface HeuristicForLogicalOptimization

_apply

protected LogicalPlan _apply(LogicalPlan inputPlan)

isProvablyEmpty

protected boolean isProvablyEmpty(LogicalPlan plan)

Returns true if, according to the cardinality estimate that has been determined for the given plan, the plan is guaranteed to produce an empty result.