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ModeShape implementation of the JCR API

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/*
 * ModeShape (http://www.modeshape.org)
 *
 * 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.modeshape.jcr.spi.index.provider;

import java.util.Map;
import javax.jcr.query.qom.Constraint;

/**
 * A simple interface that provides metrics needed to compute the cost of applying indexes.
 *
 * @author Randall Hauch ([email protected])
 */
public interface Costable {
    /**
     * Compute the cost applying the given constraint.
     *
     * @param constraint the constraint; never null
     * @param variables the bound variables for the query that is being costed; never null
     * @return the approximate number of records that will be returned
     */
    long estimateCardinality( Constraint constraint,
                              Map variables );

    /**
     * Get the estimated number of entries within this index.
     *
     * @return the number of entries, or -1 if not known
     */
    long estimateTotalCount();
}