Package com.apple.foundationdb.record.query.plan.temp

Class PlannerRule<T extends Bindable>

java.lang.Object

com.apple.foundationdb.record.query.plan.temp.PlannerRule<T>

Type Parameters:

T - a parent planner expression type of all possible root planner expressions that this rule could match

Direct Known Subclasses:

AdjustMatchRule, CombineFilterRule, DataAccessRule, FlattenNestedAndPredicateRule, FullUnorderedExpressionToScanPlanRule, ImplementDistinctRule, ImplementDistinctUnionRule, ImplementFilterRule, ImplementIndexScanRule, ImplementIntersectionRule, ImplementPhysicalScanRule, ImplementTypeFilterRule, ImplementUnorderedUnionRule, MatchIntermediateRule, MatchLeafRule, OrToUnorderedUnionRule, PushDistinctFilterBelowFilterRule, PushTypeFilterBelowFilterRule, RemoveRedundantTypeFilterRule, RemoveSortRule

@API(EXPERIMENTAL)
public abstract class PlannerRule<T extends Bindable>
extends Object

Classes that inherit from PlannerRule form the base of the Cascades planning system. During the planning process, rules are matched to a current RelationalExpression and then provide zero or more logically equivalent expressions. The rule matching occurs in two stages: first, the planner examines the matcher of the rule, which is a TypeMatcher expression that expresses the operators that the rule applies to and the hierarchical structure that they take on in the expression tree. If the rule matches the binding, its onMatch(PlannerRuleCall) method is called, with a parameter that provides the planner's PlanContext and access to the map of bindings, among other things. This method can inspect the operators bound during the structural matching and implement other logic. The onMatch() method returns logically equivalent expressions to the planner by calling the PlannerRuleCall.yield(ExpressionRef) method on its rule call, with a new ExpressionRef. The yield() method can be called more than once, or zero times if no alternative expressions are found. A rule should not attempt to modify any of the bound objects that the rule call provides. Nearly all such objects are immutable, and the mutable ones are hidden behind interfaces that do not expose mutation methods. In particular, a rule should never cast an ExpressionRef in an attempt to access it. A PlannerRule should not store state between successive calls to onMatch(PlannerRuleCall), since it may be reused an arbitrary number of times and may be reinstantiated at any time. To simplify cleanup, any state that needs to be shared within a rule call should be encapsulated in a helper object (such as a static inner class) or documented carefully.

See Also:

com.apple.foundationdb.record.query.plan.temp, PlannerRuleCall

Constructor Summary

Constructors

Constructor	Description
PlannerRule(ExpressionMatcher<T> matcher)

Method Summary

Modifier and Type	Method	Description
ExpressionMatcher<T>	getMatcher()
Optional<Class<? extends Bindable>>	getRootOperator()	Returns the class of the operator at the root of the binding expression, if this rule uses a non-trivial binding.
abstract void	onMatch(PlannerRuleCall call)
String	toString()

Methods inherited from class java.lang.Object

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

Constructor Detail

PlannerRule

public PlannerRule(@Nonnull
                   ExpressionMatcher<T> matcher)

Method Detail

getRootOperator

public Optional<Class<? extends Bindable>> getRootOperator()

Returns the class of the operator at the root of the binding expression, if this rule uses a non-trivial binding. Used primarily for indexing rules for more efficient rule search.

Returns:

the class of the root of this rule's binding, or Optional.empty() if the rule matches anything

See Also:

PlannerRuleSet

onMatch

public abstract void onMatch(@Nonnull
                             PlannerRuleCall call)

getMatcher

@Nonnull
public ExpressionMatcher<T> getMatcher()

toString

public String toString()

Overrides:

toString in class Object