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From zuyu <...@git.apache.org>
Subject [GitHub] incubator-quickstep pull request #177: Reduce the number of group-by attribu...
Date Tue, 07 Feb 2017 19:20:22 GMT
Github user zuyu commented on a diff in the pull request:

    https://github.com/apache/incubator-quickstep/pull/177#discussion_r99886212
  
    --- 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
    + *   )
    --- End diff --
    
    Do we still keep this somewhat misleading example, or will update it?


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