Github user jianqiao commented on a diff in the pull request:
https://github.com/apache/incubator-quickstep/pull/174#discussion_r98710964
--- Diff: query_optimizer/rules/PushDownLowCostDisjunctivePredicate.hpp ---
@@ -0,0 +1,118 @@
+/**
+ * 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_PUSH_DOWN_LOW_COST_DISJUNCTIVE_PREDICATE_HPP_
+#define
QUICKSTEP_QUERY_OPTIMIZER_RULES_PUSH_DOWN_LOW_COST_DISJUNCTIVE_PREDICATE_HPP_
+
+#include <cstddef>
+#include <map>
+#include <memory>
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "query_optimizer/cost_model/StarSchemaSimpleCostModel.hpp"
+#include "query_optimizer/expressions/AttributeReference.hpp"
+#include "query_optimizer/expressions/Predicate.hpp"
+#include "query_optimizer/physical/Physical.hpp"
+#include "query_optimizer/rules/Rule.hpp"
+#include "utility/Macros.hpp"
+
+namespace quickstep {
+namespace optimizer {
+
+/** \addtogroup OptimizerRules
+ * @{
+ */
+
+/**
+ * @brief Rule that applies to a physical plan to push down low-cost
disjunctive
+ * predicate when proper conditions are met.
+ *
+ * Here we elaborate the conditions.
+ *
+ * Let
+ * P = p_{1,1} AND ... AND p_{1, m_1} OR ... OR p_{n,1} AND ... AND
p_{n, m_n}
+ * be a predicate in disjunctive normal form.
+ *
+ * Now consider each small-cardinality relation R, if for each i in 1..n,
there
+ * exists at least one predicate p_{i, k_i} that is applicable to R. Then
we can
+ * construct a new predicate
+ * P' = p_{1, k_1} OR ... OR p_{n, k_n}
+ * and push down P' to be applied to R.
+ *
+ * Also, if any conjunctive component in P contains more than one
predicate that
+ * is applicable to R, then we can combine all these applicable predicates
as a
+ * conjunctive component in P'.
+ *
+ * Finally, note that if there exists a conjunctive component that
contains no
+ * predicate applicable to R. Then the condition fails and we cannot do a
push
+ * down for R.
+ */
+class PushDownLowCostDisjunctivePredicate : public
Rule<physical::Physical> {
+ public:
+ /**
+ * @brief Constructor.
+ */
+ PushDownLowCostDisjunctivePredicate() {}
+
+ ~PushDownLowCostDisjunctivePredicate() override {}
+
+ std::string getName() const override {
+ return "PushDownLowCostDisjunctivePredicate";
+ }
+
+ physical::PhysicalPtr apply(const physical::PhysicalPtr &input) override;
+
+ private:
+ struct PredicateInfo {
+ PredicateInfo() {}
+ inline void add(expressions::PredicatePtr predicate) {
+ predicates.emplace_back(predicate);
+ }
+ std::vector<expressions::PredicatePtr> predicates;
+ };
+
+ void collectApplicablePredicates(const physical::PhysicalPtr &input);
+ physical::PhysicalPtr attachPredicates(const physical::PhysicalPtr
&input) const;
--- End diff --
Updated.
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