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

Interface PlannerGraphRewritable

All Known Subinterfaces:

RecordQueryPlanWithIndex

All Known Implementing Classes:

RecordQueryIndexPlan, RecordQueryInParameterJoinPlan, RecordQueryInValuesJoinPlan, RecordQueryScanPlan, RecordQueryTextIndexPlan, RecordQueryTypeFilterPlan

public interface PlannerGraphRewritable

Interface to allow RelationalExpressions to rewrite their own graph representation. This interface allows a RelationalExpression to create/modify low level planner graph structures while a planner graph is created through an expression walk in PlannerGraphProperty. Such a rewrite can be useful if the standard representation is confusing, misleading, or just too complicated. For instance, RecordQueryPlanWithIndex additionally creates a separate node underneath the actual plan operator to show the index as a record producer. The nature of the rewrite is highly operator-specific, therefore, the rewrite is not part of the visitor or some other common logic. Expressions that decide to implement this interface must then implement rewritePlannerGraph(java.util.List<? extends com.apple.foundationdb.record.query.plan.temp.explain.PlannerGraph>) to do the actual rewrite. Implementors of this interface should rewrite the planner graph for both internal show as well as explain purposes. There are two other flavors of this interface: see InternalPlannerGraphRewritable and ExplainPlannerGraphRewritable. Those interfaces allow an expression to rewrite only for one of the use cases or differently for either of them. Note that these three interfaces do not form a hierarchy themselves. Also, in order to keep the code from bleeding into general expression structures, we didn't want to have another set of methods on RelationalExpression. The approach taken here works more like a tag interface that can be chosen by a specific operator to do something very specific without cluttering the general code path.

Method Summary

Modifier and Type	Method and Description
PlannerGraph	rewritePlannerGraph(List<? extends PlannerGraph> childGraphs) Method to rewrite the planner graph.

Method Detail

rewritePlannerGraph

@Nonnull
PlannerGraph rewritePlannerGraph(@Nonnull
                                          List<? extends PlannerGraph> childGraphs)

Method to rewrite the planner graph.

Parameters:

childGraphs - planner graphs of children expression that already have been computed

Returns:

a new planner graph that can combine the childGraphs in a meaningful way. Note that there is no obligation to use the childGraphs at all, this method can create a new independent planner graph completely from scratch.