/*
* 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.tinkerpop.gremlin.process.computer.traversal.strategy.optimization;
import org.apache.tinkerpop.gremlin.process.computer.traversal.step.map.TraversalVertexProgramStep;
import org.apache.tinkerpop.gremlin.process.computer.util.EmptyMemory;
import org.apache.tinkerpop.gremlin.process.traversal.Step;
import org.apache.tinkerpop.gremlin.process.traversal.Traversal;
import org.apache.tinkerpop.gremlin.process.traversal.TraversalStrategy;
import org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.DefaultGraphTraversal;
import org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.__;
import org.apache.tinkerpop.gremlin.process.traversal.step.Barrier;
import org.apache.tinkerpop.gremlin.process.traversal.step.LambdaHolder;
import org.apache.tinkerpop.gremlin.process.traversal.step.TraversalParent;
import org.apache.tinkerpop.gremlin.process.traversal.step.branch.LocalStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.filter.DedupGlobalStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.filter.FilterStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.map.CountGlobalStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.map.EdgeVertexStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.map.GraphStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.map.IdStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.map.TraversalFlatMapStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.map.TraversalMapStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.map.VertexStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.sideEffect.IdentityStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.sideEffect.SideEffectStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.util.EmptyStep;
import org.apache.tinkerpop.gremlin.process.traversal.strategy.AbstractTraversalStrategy;
import org.apache.tinkerpop.gremlin.process.traversal.strategy.optimization.AdjacentToIncidentStrategy;
import org.apache.tinkerpop.gremlin.process.traversal.strategy.optimization.FilterRankingStrategy;
import org.apache.tinkerpop.gremlin.process.traversal.strategy.optimization.IncidentToAdjacentStrategy;
import org.apache.tinkerpop.gremlin.process.traversal.strategy.optimization.InlineFilterStrategy;
import org.apache.tinkerpop.gremlin.process.traversal.traverser.TraverserRequirement;
import org.apache.tinkerpop.gremlin.process.traversal.util.TraversalHelper;
import org.apache.tinkerpop.gremlin.structure.Direction;
import org.apache.tinkerpop.gremlin.structure.Graph;
import org.apache.tinkerpop.gremlin.structure.util.empty.EmptyGraph;
import java.util.Arrays;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
/**
* @author Marko A. Rodriguez (http://markorodriguez.com)
*/
public final class MessagePassingReductionStrategy extends AbstractTraversalStrategy<TraversalStrategy.OptimizationStrategy> implements TraversalStrategy.OptimizationStrategy {
private static final MessagePassingReductionStrategy INSTANCE = new MessagePassingReductionStrategy();
private static final Set<Class<? extends OptimizationStrategy>> PRIORS = new HashSet<>(Arrays.asList(
IncidentToAdjacentStrategy.class,
AdjacentToIncidentStrategy.class,
FilterRankingStrategy.class,
InlineFilterStrategy.class));
private MessagePassingReductionStrategy() {
}
@Override
public void apply(final Traversal.Admin<?, ?> traversal) {
// only process the first traversal step in an OLAP chain
TraversalHelper.getFirstStepOfAssignableClass(TraversalVertexProgramStep.class, traversal).ifPresent(step -> {
final Graph graph = traversal.getGraph().orElse(EmptyGraph.instance()); // best guess at what the graph will be as its dynamically determined
final Traversal.Admin<?, ?> compiledComputerTraversal = step.generateProgram(graph, EmptyMemory.instance()).getTraversal().get().clone();
if (!compiledComputerTraversal.isLocked())
compiledComputerTraversal.applyStrategies();
if (!TraversalHelper.hasStepOfAssignableClassRecursively(Arrays.asList(LocalStep.class, LambdaHolder.class), compiledComputerTraversal) && // don't do anything with lambdas or locals as this leads to unknown adjacencies
!compiledComputerTraversal.getTraverserRequirements().contains(TraverserRequirement.PATH) && // when dynamic detachment is provided in 3.3.0, remove this (TODO)
!compiledComputerTraversal.getTraverserRequirements().contains(TraverserRequirement.LABELED_PATH) && // when dynamic detachment is provided in 3.3.0, remove this (TODO)
!(TraversalHelper.getStepsOfAssignableClass(TraversalParent.class, compiledComputerTraversal). // this is a strict precaution that could be loosed with deeper logic on barriers in global children
stream().
filter(parent -> !parent.getGlobalChildren().isEmpty()).findAny().isPresent())) {
final Traversal.Admin<?, ?> computerTraversal = step.computerTraversal.get().clone();
// apply the strategies up to this point
final List<TraversalStrategy<?>> strategies = step.getTraversal().getStrategies().toList();
final int indexOfStrategy = strategies.indexOf(MessagePassingReductionStrategy.instance());
if (indexOfStrategy > 0)
TraversalHelper.applySingleLevelStrategies(step.getTraversal(), computerTraversal, strategies.get(indexOfStrategy - 1).getClass());
if (computerTraversal.getSteps().size() > 1 &&
!(computerTraversal.getStartStep().getNextStep() instanceof Barrier) &&
TraversalHelper.hasStepOfAssignableClassRecursively(Arrays.asList(VertexStep.class, EdgeVertexStep.class), computerTraversal) &&
TraversalHelper.isLocalStarGraph(computerTraversal)) {
final Step barrier = (Step) TraversalHelper.getFirstStepOfAssignableClass(Barrier.class, computerTraversal).orElse(null);
if (MessagePassingReductionStrategy.insertElementId(barrier)) // out().count() -> out().id().count()
TraversalHelper.insertBeforeStep(new IdStep(computerTraversal), barrier, computerTraversal);
if (!(MessagePassingReductionStrategy.endsWithElement(null == barrier ? computerTraversal.getEndStep() : barrier))) {
Traversal.Admin newChildTraversal = new DefaultGraphTraversal<>();
TraversalHelper.removeToTraversal(computerTraversal.getStartStep() instanceof GraphStep ?
computerTraversal.getStartStep().getNextStep() :
(Step) computerTraversal.getStartStep(), null == barrier ?
EmptyStep.instance() :
barrier, newChildTraversal);
newChildTraversal = newChildTraversal.getSteps().size() > 1 ? (Traversal.Admin) __.local(newChildTraversal) : newChildTraversal;
if (null == barrier)
TraversalHelper.insertTraversal(0, newChildTraversal, computerTraversal);
else
TraversalHelper.insertTraversal(barrier.getPreviousStep(), newChildTraversal, computerTraversal);
}
}
step.setComputerTraversal(computerTraversal);
}
});
}
private static boolean insertElementId(final Step<?, ?> barrier) {
if (!(barrier instanceof Barrier))
return false;
else if (!endsWithElement(barrier.getPreviousStep()))
return false;
else if (barrier instanceof CountGlobalStep)
return true;
else if (barrier instanceof DedupGlobalStep &&
((DedupGlobalStep) barrier).getScopeKeys().isEmpty() &&
((DedupGlobalStep) barrier).getLocalChildren().isEmpty() &&
barrier.getNextStep() instanceof CountGlobalStep)
return true;
else
return false;
}
public static final boolean endsWithElement(Step<?, ?> currentStep) {
while (!(currentStep instanceof EmptyStep)) {
if (currentStep instanceof VertexStep) // only inE, in, and out send messages
return (((VertexStep) currentStep).returnsVertex() || !((VertexStep) currentStep).getDirection().equals(Direction.OUT));
else if (currentStep instanceof EdgeVertexStep) // TODO: add GraphStep but only if its mid-traversal V()/E()
return true;
else if (currentStep instanceof TraversalFlatMapStep || currentStep instanceof TraversalMapStep || currentStep instanceof LocalStep)
return endsWithElement(((TraversalParent) currentStep).getLocalChildren().get(0).getEndStep());
else if (!(currentStep instanceof FilterStep || currentStep instanceof SideEffectStep || currentStep instanceof IdentityStep || currentStep instanceof Barrier))
return false;
currentStep = currentStep.getPreviousStep();
}
return false;
}
@Override
public Set<Class<? extends OptimizationStrategy>> applyPrior() {
return PRIORS;
}
public static MessagePassingReductionStrategy instance() {
return INSTANCE;
}
}