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1   /*
2    *   Copyright 2004 The Apache Software Foundation
3    *
4    *   Licensed under the Apache License, Version 2.0 (the "License");
5    *   you may not use this file except in compliance with the License.
6    *   You may obtain a copy of the License at
7    *
8    *       http://www.apache.org/licenses/LICENSE-2.0
9    *
10   *   Unless required by applicable law or agreed to in writing, software
11   *   distributed under the License is distributed on an "AS IS" BASIS,
12   *   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13   *   See the License for the specific language governing permissions and
14   *   limitations under the License.
15   *
16   */
17  package org.apache.ldap.server.partition.impl.btree;
18  
19  
20  import javax.naming.NamingException;
21  
22  import org.apache.ldap.common.filter.ExprNode;
23  
24  
25  /***
26   * An optimizer applies heuristics to determine best execution path to a search
27   * filter based on scan counts within database indices.  It annotates the nodes
28   * of an expression subtree by setting a "count" key in the node.  Its goal is
29   * to annotate nodes with counts to indicate which nodes to iterate over thereby
30   * minimizing the number cycles in a search.  The SearchEngine relies on these
31   * count markers to determine the appropriate path.
32   * 
33   * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
34   * @version $Rev: 264732 $
35   */
36  public interface Optimizer
37  {
38      /***
39       * Annotates the expression node tree for optimized traversal metrics.
40       *
41       * @param node the root of the expression node tree
42       * @throws NamingException if there are failures while optimizing
43       */
44      void annotate( ExprNode node ) throws NamingException;
45  }