001    /*
002     *  Licensed to the Apache Software Foundation (ASF) under one
003     *  or more contributor license agreements.  See the NOTICE file
004     *  distributed with this work for additional information
005     *  regarding copyright ownership.  The ASF licenses this file
006     *  to you under the Apache License, Version 2.0 (the
007     *  "License"); you may not use this file except in compliance
008     *  with the License.  You may obtain a copy of the License at
009     *  
010     *    http://www.apache.org/licenses/LICENSE-2.0
011     *  
012     *  Unless required by applicable law or agreed to in writing,
013     *  software distributed under the License is distributed on an
014     *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015     *  KIND, either express or implied.  See the License for the
016     *  specific language governing permissions and limitations
017     *  under the License. 
018     *  
019     */
020    package org.apache.directory.server.xdbm.search;
021    
022    
023    import org.apache.directory.shared.ldap.filter.ExprNode;
024    
025    
026    /**
027     * An optimizer applies heuristics to determine best execution path to a search
028     * filter based on scan counts within database indices.  It annotates the nodes
029     * of an expression subtree by setting a "count" key in the node.  Its goal is
030     * to annotate nodes with counts to indicate which nodes to iterate over thereby
031     * minimizing the number cycles in a search.  The SearchEngine relies on these
032     * count markers to determine the appropriate path.
033     * 
034     * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
035     * @version $Rev: 656041 $
036     */
037    public interface Optimizer
038    {
039        /**
040         * Annotates the expression node tree for optimized traversal metrics.
041         *
042         * @param node the root of the expression node tree
043         * @throws Exception if there are failures while optimizing
044         */
045        Long annotate( ExprNode node ) throws Exception;
046    }