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From zuyu <...@git.apache.org>
Subject [GitHub] incubator-quickstep pull request #177: Reduce the number of group-by attribu...
Date Wed, 08 Feb 2017 00:18:14 GMT
Github user zuyu commented on a diff in the pull request:

    https://github.com/apache/incubator-quickstep/pull/177#discussion_r99964669
  
    --- Diff: query_optimizer/rules/ReduceGroupByAttributes.hpp ---
    @@ -0,0 +1,143 @@
    +/**
    + * 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_REDUCE_GROUP_BY_ATTRIBUTES_HPP_
    +#define QUICKSTEP_QUERY_OPTIMIZER_RULES_REDUCE_GROUP_BY_ATTRIBUTES_HPP_
    +
    +#include <cstddef>
    +#include <memory>
    +#include <string>
    +#include <unordered_map>
    +#include <utility>
    +
    +#include "query_optimizer/cost_model/StarSchemaSimpleCostModel.hpp"
    +#include "query_optimizer/expressions/AttributeReference.hpp"
    +#include "query_optimizer/expressions/ExprId.hpp"
    +#include "query_optimizer/physical/Physical.hpp"
    +#include "query_optimizer/physical/TableReference.hpp"
    +#include "query_optimizer/rules/Rule.hpp"
    +#include "utility/Macros.hpp"
    +
    +namespace quickstep {
    +namespace optimizer {
    +
    +class OptimizerContext;
    +
    +/**
    + * @brief Rule that applies to a physical plan to reduce the number of group-by
    + *        attributes for Aggregate nodes (to improve performance) by pulling
    + *        joins up the aggregations.
    + *
    + * For example, let R be a relation with PRIMARY KEY x and attributes y, z. Let
    + * S be a relation with FOREIGN KEY u refering to R(x) and attribute v. Then the
    + * optimization rule will transform the physical plan:
    + *   Aggregate(
    + *     [input relation]: HashJoin(
    + *                         [probe relation]: S
    + *                         [build relation]: R
    + *                         [join expression]: S.u = R.x
    + *                         [project attributes]: v, x, y, z
    + *                       )
    + *     [aggregate expression]: SUM(v) AS sum_v
    + *     [group-by attributes]: x, y, z
    + *   )
    + *
    + * into:
    + *   HashJoin(
    + *     [probe relation]: Aggregate(
    + *                         [input relation]: S
    + *                         [aggregate expression]: SUM(v) AS sum_v
    + *                         [group-by attribute]: u
    + *                       ) AS T
    + *     [build relation]: R
    + *     [join expression]: T.u = R.x
    + *     [project attributes]: sum_v, x, y, z
    + *   )
    + */
    +class ReduceGroupByAttributes : public Rule<physical::Physical> {
    + public:
    +  /**
    +   * @brief Constructor.
    +   *
    +   * @param optimizer_context The optimizer context.
    +   */
    +  explicit ReduceGroupByAttributes(OptimizerContext *optimizer_context)
    +      : optimizer_context_(optimizer_context) {}
    +
    +  ~ReduceGroupByAttributes() override {}
    +
    +  std::string getName() const override {
    +    return "ReduceGroupByAttributes";
    +  }
    +
    +  physical::PhysicalPtr apply(const physical::PhysicalPtr &input) override;
    +
    + private:
    +  struct AttributeInfo {
    +    AttributeInfo(const expressions::AttributeReferencePtr &attribute_in,
    +                  const bool is_unique_in,
    +                  const bool is_fixed_length_in,
    +                  const std::size_t maximum_size_in)
    +        : attribute(attribute_in),
    +          is_unique(is_unique_in),
    +          is_fixed_length(is_fixed_length_in),
    +          maximum_size(maximum_size_in) {}
    +
    +    // In the situation that there are multiple attributes that can serve as the
    +    // group-by key, we define an ordering based on aggregation performance (e.g.
    +    // it is faster to do aggregation with a fix-length attribute as the group-by
    +    // key than with a variable-length attribute).
    +    inline static bool IsBetterThan(const AttributeInfo *lhs,
    +                                    const AttributeInfo *rhs) {
    +      if (lhs->is_unique != rhs->is_unique) {
    +        return lhs->is_unique;
    +      }
    +      if (lhs->is_fixed_length != rhs->is_fixed_length) {
    +        return lhs->is_fixed_length;
    +      }
    +      if (lhs->maximum_size != rhs->maximum_size) {
    +        return lhs->maximum_size < rhs->maximum_size;
    +      }
    +      return lhs->attribute->id() < rhs->attribute->id();
    +    }
    +
    +    const expressions::AttributeReferencePtr attribute;
    +    const bool is_unique;
    +    const bool is_fixed_length;
    +    const std::size_t maximum_size;
    --- End diff --
    
    Then, please rename to `maximum_byte_length`, as defined in `Type`.


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