org.apache.calcite.plan.volcano.VolcanoRelMetadataProvider.java Source code

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Here is the source code for org.apache.calcite.plan.volcano.VolcanoRelMetadataProvider.java

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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.calcite.plan.volcano;

import org.apache.calcite.rel.RelNode;
import org.apache.calcite.rel.metadata.Metadata;
import org.apache.calcite.rel.metadata.MetadataDef;
import org.apache.calcite.rel.metadata.MetadataHandler;
import org.apache.calcite.rel.metadata.RelMetadataProvider;
import org.apache.calcite.rel.metadata.RelMetadataQuery;
import org.apache.calcite.rel.metadata.UnboundMetadata;

import com.google.common.collect.ImmutableMultimap;
import com.google.common.collect.Multimap;

import java.lang.reflect.Method;

/**
 * VolcanoRelMetadataProvider implements the {@link RelMetadataProvider}
 * interface by combining metadata from the rels making up an equivalence class.
 */
public class VolcanoRelMetadataProvider implements RelMetadataProvider {
    //~ Methods ----------------------------------------------------------------

    @Override
    public boolean equals(Object obj) {
        return obj instanceof VolcanoRelMetadataProvider;
    }

    @Override
    public int hashCode() {
        return 103;
    }

    public <M extends Metadata> UnboundMetadata<M> apply(Class<? extends RelNode> relClass,
            final Class<? extends M> metadataClass) {
        if (relClass != RelSubset.class) {
            // let someone else further down the chain sort it out
            return null;
        }

        return new UnboundMetadata<M>() {
            public M bind(RelNode rel, RelMetadataQuery mq) {
                final RelSubset subset = (RelSubset) rel;
                final RelMetadataProvider provider = rel.getCluster().getMetadataProvider();

                // REVIEW jvs 29-Mar-2006: I'm not sure what the correct precedence
                // should be here.  Letting the current best plan take the first shot is
                // probably the right thing to do for physical estimates such as row
                // count.  Dunno about others, and whether we need a way to
                // discriminate.

                // First, try current best implementation.  If it knows how to answer
                // this query, treat it as the most reliable.
                if (subset.best != null) {
                    final UnboundMetadata<M> function = provider.apply(subset.best.getClass(), metadataClass);
                    if (function != null) {
                        final M metadata = function.bind(subset.best, mq);
                        if (metadata != null) {
                            return metadata;
                        }
                    }
                }

                // Otherwise, try rels in same logical equivalence class to see if any
                // of them have a good answer.  We use the full logical equivalence
                // class rather than just the subset because many metadata providers
                // only know about logical metadata.

                // Equivalence classes can get tangled up in interesting ways, so avoid
                // an infinite loop.  REVIEW: There's a chance this will cause us to
                // fail on metadata queries which invoke other queries, e.g.
                // PercentageOriginalRows -> Selectivity.  If we implement caching at
                // this level, we could probably kill two birds with one stone (use
                // presence of pending cache entry to detect re-entrancy at the correct
                // granularity).
                if (subset.set.inMetadataQuery) {
                    return null;
                }

                subset.set.inMetadataQuery = true;
                try {
                    for (RelNode relCandidate : subset.set.rels) {
                        final UnboundMetadata<M> function = provider.apply(relCandidate.getClass(), metadataClass);
                        if (function != null) {
                            final M result = function.bind(relCandidate, mq);
                            if (result != null) {
                                return result;
                            }
                        }
                    }
                } finally {
                    subset.set.inMetadataQuery = false;
                }

                // Give up.
                return null;
            }
        };
    }

    public <M extends Metadata> Multimap<Method, MetadataHandler<M>> handlers(MetadataDef<M> def) {
        return ImmutableMultimap.of();
    }
}

// End VolcanoRelMetadataProvider.java