| /** |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF licenses this file |
| * to you 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. |
| **/ |
| |
| #ifndef QUICKSTEP_QUERY_OPTIMIZER_RULES_TOP_DOWN_RULE_HPP_ |
| #define QUICKSTEP_QUERY_OPTIMIZER_RULES_TOP_DOWN_RULE_HPP_ |
| |
| #include <memory> |
| #include <vector> |
| |
| #include "query_optimizer/rules/Rule.hpp" |
| #include "utility/Macros.hpp" |
| |
| #include "glog/logging.h" |
| |
| namespace quickstep { |
| namespace optimizer { |
| |
| /** \addtogroup OptimizerRules |
| * @{ |
| */ |
| |
| /** |
| * @brief Base class for a rule that performs a top-down traverse on a tree. |
| */ |
| template <class TreeType> |
| class TopDownRule : public Rule<TreeType> { |
| public: |
| typedef std::shared_ptr<const TreeType> TreeNodePtr; |
| |
| /** |
| * @brief Constructor. |
| */ |
| TopDownRule() {} |
| |
| /** |
| * @brief Destructor. |
| */ |
| ~TopDownRule() override {} |
| |
| TreeNodePtr apply(const TreeNodePtr &tree) override { |
| DCHECK(tree != nullptr); |
| TreeNodePtr new_tree; |
| |
| new_tree = applyToNode(tree); |
| DCHECK(new_tree != nullptr); |
| |
| // TODO(qzeng): We assume that the ordering of the children is irrelevant, |
| // but this may not be true for TopLevelPlan if we implement some rules |
| // (e.g. outer-join elimination) that may change the output attributes of |
| // a query plan. For a top-down traverse, the least dependent shared |
| // subplan should be the last one to be processed, while it should be |
| // visited first for a bottom-up traverse. |
| std::vector<TreeNodePtr> new_children; |
| bool has_changed_children = false; |
| const std::vector<TreeNodePtr> ¤t_children = new_tree->children(); |
| for (const TreeNodePtr ¤t_child : current_children) { |
| TreeNodePtr new_child; |
| new_child = apply(current_child); |
| if (current_child != new_child && !has_changed_children) { |
| has_changed_children = true; |
| } |
| new_children.push_back(new_child); |
| } |
| |
| if (has_changed_children) { |
| new_tree = new_tree->copyWithNewChildren(new_children); |
| } |
| |
| return new_tree; |
| } |
| |
| protected: |
| /** |
| * @brief Applies the rule to a single node, not the entire tree. |
| * |
| * @param node The node to apply the rule to. |
| * @param The updated node by the rule. |
| */ |
| virtual TreeNodePtr applyToNode(const TreeNodePtr &node) = 0; |
| |
| private: |
| DISALLOW_COPY_AND_ASSIGN(TopDownRule); |
| }; |
| |
| /** @} */ |
| |
| } // namespace optimizer |
| } // namespace quickstep |
| |
| #endif /* QUICKSTEP_QUERY_OPTIMIZER_RULES_TOP_DOWN_RULE_HPP_ */ |