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1   /*
2    *  Licensed to the Apache Software Foundation (ASF) under one
3    *  or more contributor license agreements.  See the NOTICE file
4    *  distributed with this work for additional information
5    *  regarding copyright ownership.  The ASF licenses this file
6    *  to you under the Apache License, Version 2.0 (the
7    *  "License"); you may not use this file except in compliance
8    *  with the License.  You may obtain a copy of the License at
9    *  
10   *    http://www.apache.org/licenses/LICENSE-2.0
11   *  
12   *  Unless required by applicable law or agreed to in writing,
13   *  software distributed under the License is distributed on an
14   *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
15   *  KIND, either express or implied.  See the License for the
16   *  specific language governing permissions and limitations
17   *  under the License. 
18   *  
19   */
20  package org.apache.directory.server.xdbm.search;
21  
22  
23  import org.apache.directory.shared.ldap.filter.ExprNode;
24  
25  
26  /**
27   * An optimizer applies heuristics to determine best execution path to a search
28   * filter based on scan counts within database indices.  It annotates the nodes
29   * of an expression subtree by setting a "count" key in the node.  Its goal is
30   * to annotate nodes with counts to indicate which nodes to iterate over thereby
31   * minimizing the number cycles in a search.  The SearchEngine relies on these
32   * count markers to determine the appropriate path.
33   * 
34   * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
35   * @version $Rev: 656041 $
36   */
37  public interface Optimizer
38  {
39      /**
40       * Annotates the expression node tree for optimized traversal metrics.
41       *
42       * @param node the root of the expression node tree
43       * @throws Exception if there are failures while optimizing
44       */
45      Long annotate( ExprNode node ) throws Exception;
46  }