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* 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.traversal.strategy.optimization;
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.step.LambdaHolder;
import org.apache.tinkerpop.gremlin.process.traversal.step.Scoping;
import org.apache.tinkerpop.gremlin.process.traversal.step.TraversalParent;
import org.apache.tinkerpop.gremlin.process.traversal.step.filter.AndStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.filter.ClassFilterStep;
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.filter.HasStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.filter.IsStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.filter.NotStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.filter.OrStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.filter.TraversalFilterStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.filter.WherePredicateStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.filter.WhereTraversalStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.map.OrderGlobalStep;
import org.apache.tinkerpop.gremlin.process.traversal.strategy.AbstractTraversalStrategy;
import org.apache.tinkerpop.gremlin.process.traversal.util.TraversalHelper;
import java.util.Collections;
import java.util.List;
import java.util.Set;
/**
* FilterRankingStrategy reorders filter- and order-steps according to their rank. It will also do its best to push
* step labels as far "right" as possible in order to keep traversers as small and bulkable as possible prior to the
* absolute need for path-labeling.
*
* @author Daniel Kuppitz (http://gremlin.guru)
* @author Marko A. Rodriguez (http://markorodriguez.com)
* @example <pre>
* __.order().dedup() // is replaced by __.dedup().order()
* __.dedup().filter(out()).has("value", 0) // is replaced by __.has("value", 0).filter(out()).dedup()
* </pre>
*/
public final class FilterRankingStrategy extends AbstractTraversalStrategy<TraversalStrategy.OptimizationStrategy> implements TraversalStrategy.OptimizationStrategy {
private static final FilterRankingStrategy INSTANCE = new FilterRankingStrategy();
private static final Set<Class<? extends OptimizationStrategy>> PRIORS = Collections.singleton(IdentityRemovalStrategy.class);
private FilterRankingStrategy() {
}
@Override
public void apply(final Traversal.Admin<?, ?> traversal) {
boolean modified = true;
while (modified) {
modified = false;
final List<Step> steps = traversal.getSteps();
for (int i = 0; i < steps.size() - 1; i++) {
final Step<?, ?> step = steps.get(i);
final Step<?, ?> nextStep = step.getNextStep();
if (!usesLabels(nextStep, step.getLabels())) {
final int nextRank = getStepRank(nextStep);
if (nextRank != 0) {
if (!step.getLabels().isEmpty()) {
TraversalHelper.copyLabels(step, nextStep, true);
modified = true;
}
if (getStepRank(step) > nextRank) {
traversal.removeStep(nextStep);
traversal.addStep(i, nextStep);
modified = true;
}
}
}
}
}
}
/**
* Ranks the given step. Steps with lower ranks can be moved in front of steps with higher ranks. 0 means that
* the step has no rank and thus is not exchangeable with its neighbors.
*
* @param step the step to get a ranking for
* @return The rank of the given step.
*/
private static int getStepRank(final Step step) {
final int rank;
if (!(step instanceof FilterStep || step instanceof OrderGlobalStep))
return 0;
else if (step instanceof IsStep || step instanceof ClassFilterStep)
rank = 1;
else if (step instanceof HasStep)
rank = 2;
else if (step instanceof WherePredicateStep && ((WherePredicateStep) step).getLocalChildren().isEmpty())
rank = 3;
else if (step instanceof TraversalFilterStep || step instanceof NotStep)
rank = 4;
else if (step instanceof WhereTraversalStep)
rank = 5;
else if (step instanceof OrStep)
rank = 6;
else if (step instanceof AndStep)
rank = 7;
else if (step instanceof WherePredicateStep) // has by()-modulation
rank = 8;
else if (step instanceof DedupGlobalStep)
rank = 9;
else if (step instanceof OrderGlobalStep)
rank = 10;
else
return 0;
////////////
if (step instanceof TraversalParent)
return getMaxStepRank((TraversalParent) step, rank);
else
return rank;
}
private static int getMaxStepRank(final TraversalParent parent, final int startRank) {
int maxStepRank = startRank;
// no filter steps are global parents (yet)
for (final Traversal.Admin<?, ?> traversal : parent.getLocalChildren()) {
for (final Step<?, ?> step : traversal.getSteps()) {
final int stepRank = getStepRank(step);
if (stepRank > maxStepRank)
maxStepRank = stepRank;
}
}
return maxStepRank;
}
private static boolean usesLabels(final Step<?, ?> step, final Set<String> labels) {
if (step instanceof LambdaHolder)
return true;
if (step instanceof Scoping) {
final Set<String> scopes = ((Scoping) step).getScopeKeys();
for (final String label : labels) {
if (scopes.contains(label))
return true;
}
}
if (step instanceof TraversalParent) {
if (TraversalHelper.anyStepRecursively(s -> usesLabels(s, labels), (TraversalParent) step))
return true;
}
return false;
}
@Override
public Set<Class<? extends OptimizationStrategy>> applyPrior() {
return PRIORS;
}
public static FilterRankingStrategy instance() {
return INSTANCE;
}
}