org.usergrid.persistence.query.ir.result.IntersectionIterator.java Source code

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Here is the source code for org.usergrid.persistence.query.ir.result.IntersectionIterator.java

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/*******************************************************************************
 * Copyright 2012 Apigee Corporation
 * 
 * Licensed 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.usergrid.persistence.query.ir.result;

import java.util.LinkedHashSet;
import java.util.Set;
import java.util.UUID;

import org.usergrid.persistence.cassandra.CursorCache;

import com.google.common.collect.Sets;

/**
 * An iterator that unions 1 or more subsets. It makes the assuming that sub
 * iterators iterate from min(uuid) to max(uuid)
 * 
 * @author tnine
 * 
 */
public class IntersectionIterator extends MultiIterator {

    /**
     * 
     */
    public IntersectionIterator(int pageSize) {
        super(pageSize);
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.usergrid.persistence.query.ir.result.ResultIterator#reset()
     */
    @Override
    public void doReset() {
        for (ResultIterator itr : iterators) {
            itr.reset();
        }
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.usergrid.persistence.query.ir.result.MergeIterator#advance()
     */
    @Override
    protected Set<UUID> advance() {
        /**
         * Advance our sub iterators until the UUID's all line up
         */

        int size = iterators.size();

        if (size == 0) {
            return null;
        }

        // edge case with only 1 iterator
        if (size == 1) {

            ResultIterator itr = iterators.get(0);

            if (!itr.hasNext()) {
                return null;
            }

            return itr.next();
        }

        // begin our tree merge of the iterators

        return merge();

    }

    private Set<UUID> merge() {

        Set<UUID> results = new LinkedHashSet<UUID>();
        ResultIterator rootIterator = iterators.get(0);

        //we've matched to the end
        if (!rootIterator.hasNext()) {
            return null;
        }

        //purposely check size first, that way we avoid another round trip if we can
        while (results.size() < pageSize && rootIterator.hasNext()) {

            Set<UUID> intersection = rootIterator.next();

            for (int i = 1; i < iterators.size(); i++) {

                ResultIterator joinIterator = iterators.get(i);

                intersection = merge(intersection, joinIterator);

                //nothing left short circuit, there is no point in advancing to further join iterators
                if (intersection.size() == 0) {
                    break;
                }
            }

            //now add the intermediate results and continue
            results.addAll(intersection);
        }

        return results;

    }

    private Set<UUID> merge(Set<UUID> current, ResultIterator child) {

        Set<UUID> results = new LinkedHashSet<UUID>(pageSize);

        while (results.size() < pageSize) {
            if (!child.hasNext()) {
                // we've iterated to the end, reset for next pass
                child.reset();
                return results;
            }

            results.addAll(Sets.intersection(current, child.next()));
        }

        return results;

    }

    /*
     * (non-Javadoc)
     * 
     * @see
     * org.usergrid.persistence.query.ir.result.ResultIterator#finalizeCursor(
     * org.usergrid.persistence.cassandra.CursorCache)
     */
    @Override
    public void finalizeCursor(CursorCache cache, UUID lastLoaded) {
        ResultIterator itr = iterators.get(0);

        //We can only create a cursor on our root level value in the intersection iterator.
        if (itr != null) {
            itr.finalizeCursor(cache, lastLoaded);
        }
    }

}