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1   /*
2    * ModeShape (http://www.modeshape.org)
3    * See the COPYRIGHT.txt file distributed with this work for information
4    * regarding copyright ownership.  Some portions may be licensed
5    * to Red Hat, Inc. under one or more contributor license agreements.
6    * See the AUTHORS.txt file in the distribution for a full listing of 
7    * individual contributors.
8    *
9    * ModeShape is free software. Unless otherwise indicated, all code in ModeShape
10   * is licensed to you under the terms of the GNU Lesser General Public License as
11   * published by the Free Software Foundation; either version 2.1 of
12   * the License, or (at your option) any later version.
13   * 
14   * ModeShape is distributed in the hope that it will be useful,
15   * but WITHOUT ANY WARRANTY; without even the implied warranty of
16   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
17   * Lesser General Public License for more details.
18   *
19   * You should have received a copy of the GNU Lesser General Public
20   * License along with this software; if not, write to the Free
21   * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
22   * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
23   */
24  package org.modeshape.graph.query.optimize;
25  
26  import java.util.LinkedList;
27  import net.jcip.annotations.Immutable;
28  import org.modeshape.common.collection.Problems;
29  import org.modeshape.common.util.Logger;
30  import org.modeshape.graph.query.QueryContext;
31  import org.modeshape.graph.query.plan.PlanHints;
32  import org.modeshape.graph.query.plan.PlanNode;
33  
34  /**
35   * Optimizer implementation that optimizes a query using a stack of rules. Subclasses can override the
36   * {@link #populateRuleStack(LinkedList, PlanHints)} method to define the stack of rules they'd like to use, including the use of
37   * custom rules.
38   */
39  @Immutable
40  public class RuleBasedOptimizer implements Optimizer {
41  
42      private static final Logger LOGGER = Logger.getLogger(RuleBasedOptimizer.class);
43  
44      /**
45       * {@inheritDoc}
46       * 
47       * @see org.modeshape.graph.query.optimize.Optimizer#optimize(QueryContext, PlanNode)
48       */
49      public PlanNode optimize( QueryContext context,
50                                PlanNode plan ) {
51          LinkedList<OptimizerRule> rules = new LinkedList<OptimizerRule>();
52          populateRuleStack(rules, context.getHints());
53  
54          Problems problems = context.getProblems();
55          while (rules.peek() != null && !problems.hasErrors()) {
56              OptimizerRule nextRule = rules.poll();
57              LOGGER.debug("Running query optimizer rule {0}", nextRule);
58              plan = nextRule.execute(context, plan, rules);
59          }
60  
61          return plan;
62      }
63  
64      /**
65       * Method that is used to create the initial rule stack. This method can be overridden by subclasses
66       * 
67       * @param ruleStack the stack where the rules should be placed; never null
68       * @param hints the plan hints
69       */
70      protected void populateRuleStack( LinkedList<OptimizerRule> ruleStack,
71                                        PlanHints hints ) {
72          ruleStack.addFirst(ReplaceAliases.INSTANCE);
73          ruleStack.addFirst(RewriteAsRangeCriteria.INSTANCE);
74          if (hints.hasJoin) {
75              ruleStack.addFirst(ChooseJoinAlgorithm.USE_ONLY_NESTED_JOIN_ALGORITHM);
76              ruleStack.addFirst(RewriteIdentityJoins.INSTANCE);
77          }
78          ruleStack.addFirst(PushProjects.INSTANCE);
79          ruleStack.addFirst(PushSelectCriteria.INSTANCE);
80          ruleStack.addFirst(AddAccessNodes.INSTANCE);
81          ruleStack.addFirst(RightOuterToLeftOuterJoins.INSTANCE);
82          ruleStack.addFirst(CopyCriteria.INSTANCE);
83          if (hints.hasView) {
84              ruleStack.addFirst(ReplaceViews.INSTANCE);
85          }
86      }
87  }