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From jianqiao <...@git.apache.org>
Subject [GitHub] incubator-quickstep pull request #177: Reduce the number of group-by attribu...
Date Tue, 07 Feb 2017 16:34:18 GMT
Github user jianqiao commented on a diff in the pull request:

    https://github.com/apache/incubator-quickstep/pull/177#discussion_r99865239
  
    --- Diff: query_optimizer/rules/ReduceGroupByAttributes.cpp ---
    @@ -0,0 +1,217 @@
    +/**
    + * 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.
    + **/
    +
    +#include "query_optimizer/rules/ReduceGroupByAttributes.hpp"
    +
    +#include <algorithm>
    +#include <map>
    +#include <vector>
    +#include <unordered_set>
    +#include <utility>
    +
    +#include "catalog/CatalogRelation.hpp"
    +#include "query_optimizer/OptimizerContext.hpp"
    +#include "query_optimizer/cost_model/StarSchemaSimpleCostModel.hpp"
    +#include "query_optimizer/expressions/AttributeReference.hpp"
    +#include "query_optimizer/expressions/ExprId.hpp"
    +#include "query_optimizer/expressions/ExpressionUtil.hpp"
    +#include "query_optimizer/expressions/NamedExpression.hpp"
    +#include "query_optimizer/physical/Aggregate.hpp"
    +#include "query_optimizer/physical/HashJoin.hpp"
    +#include "query_optimizer/physical/PatternMatcher.hpp"
    +#include "query_optimizer/physical/Physical.hpp"
    +#include "query_optimizer/physical/PhysicalType.hpp"
    +#include "query_optimizer/physical/TableReference.hpp"
    +#include "query_optimizer/physical/TopLevelPlan.hpp"
    +#include "query_optimizer/rules/PruneColumns.hpp"
    +
    +#include "gflags/gflags.h"
    +
    +#include "glog/logging.h"
    +
    +namespace quickstep {
    +namespace optimizer {
    +
    +DEFINE_uint64(reduce_group_by_attributes_threshold, 3u,
    +              "The threshold for a stored relation's number of attributes in a "
    +              "group-by clause for the ReduceGroupByAttributes optimization "
    +              "rule to pull the stored relation up the aggregation");
    +
    +namespace E = ::quickstep::optimizer::expressions;
    +namespace P = ::quickstep::optimizer::physical;
    +
    +P::PhysicalPtr ReduceGroupByAttributes::apply(const P::PhysicalPtr &input) {
    +  DCHECK(input->getPhysicalType() == P::PhysicalType::kTopLevelPlan);
    +  cost_model_.reset(new cost::StarSchemaSimpleCostModel(
    +      std::static_pointer_cast<const P::TopLevelPlan>(input)->shared_subplans()));
    +
    +  P::PhysicalPtr output = applyInternal(input);
    +  if (output != input) {
    +    output = PruneColumns().apply(output);
    +  }
    +  return output;
    +}
    +
    +P::PhysicalPtr ReduceGroupByAttributes::applyInternal(const P::PhysicalPtr &input)
{
    +  std::vector<P::PhysicalPtr> new_children;
    +  for (const P::PhysicalPtr &child : input->children()) {
    +    new_children.push_back(applyInternal(child));
    +  }
    +
    +  if (new_children != input->children()) {
    +    return applyToNode(input->copyWithNewChildren(new_children));
    +  } else {
    +    return applyToNode(input);
    +  }
    +}
    +
    +P::PhysicalPtr ReduceGroupByAttributes::applyToNode(const P::PhysicalPtr &input)
{
    +  P::TableReferencePtr table_reference;
    +  if (P::SomeTableReference::MatchesWithConditionalCast(input, &table_reference))
{
    +    // Collect the attributes-to-TableReference mapping info.
    +    for (const auto &attr : table_reference->attribute_list()) {
    +      source_.emplace(attr->id(), std::make_pair(table_reference, attr));
    +    }
    +    return input;
    +  }
    +
    +  P::AggregatePtr aggregate;
    +  if (!P::SomeAggregate::MatchesWithConditionalCast(input, &aggregate) ||
    +      aggregate->grouping_expressions().size() <= 1u) {
    +    return input;
    +  }
    +
    +  // Divide the group-by attributes into groups based on their source table.
    +  std::map<P::TableReferencePtr, std::vector<E::AttributeReferencePtr>> table_attributes;
    --- End diff --
    
    We would expect tables attributes to contain a small number of entries (# of storage tables
for the attributes in one group-by clause, typically 1 to 3). Also consider that there an
iteration of all the map elements below. It might be better to use a `std::map` here. Anyway
it won't make even a tiny performance difference to use either data structure here.


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