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From hbdeshmukh <...@git.apache.org>
Subject [GitHub] incubator-quickstep pull request #181: Added limited optimizer support for P...
Date Tue, 07 Mar 2017 02:06:44 GMT
Github user hbdeshmukh commented on a diff in the pull request:

    https://github.com/apache/incubator-quickstep/pull/181#discussion_r104573872
  
    --- Diff: query_optimizer/ExecutionGenerator.cpp ---
    @@ -679,13 +688,72 @@ void ExecutionGenerator::convertFilterJoin(const P::FilterJoinPtr
&physical_plan
           std::piecewise_construct,
           std::forward_as_tuple(physical_plan),
           std::forward_as_tuple(probe_relation_info->producer_operator_index,
    -                            probe_relation_info->relation));
    +                            probe_relation_info->relation,
    +                            probe_relation_info->output_destination_index));
     
       DCHECK(lip_filter_generator_ != nullptr);
       lip_filter_generator_->addFilterJoinInfo(physical_plan,
                                                build_filter_operator_index);
     }
     
    +namespace {
    +
    +bool areSamePartitionSchemeHeaders(const PartitionSchemeHeader &lhs_partition_header,
    +                                   const CatalogRelationSchema &lhs_scheme,
    +                                   const PartitionSchemeHeader &rhs_partition_header,
    +                                   const CatalogRelationSchema &rhs_scheme) {
    +  if (lhs_partition_header.getPartitionType() != rhs_partition_header.getPartitionType())
{
    +    return false;
    +  }
    +
    +  if (lhs_partition_header.getNumPartitions() != rhs_partition_header.getNumPartitions())
{
    +    return false;
    +  }
    +
    +  // Check whether the underlying types in CatalogAttribute are the same.
    +  if (!lhs_scheme.getAttributeById(lhs_partition_header.getPartitionAttributeId())->getType().equals(
    +       rhs_scheme.getAttributeById(rhs_partition_header.getPartitionAttributeId())->getType()))
{
    +    return false;
    +  }
    +
    +  switch (lhs_partition_header.getPartitionType()) {
    +    case PartitionSchemeHeader::PartitionType::kHash:
    +      return true;
    +    case PartitionSchemeHeader::PartitionType::kRange: {
    +      const vector<TypedValue> &lhs_ranges =
    +          static_cast<const RangePartitionSchemeHeader&>(lhs_partition_header).getPartitionRangeBoundaries();
    +      const vector<TypedValue> &rhs_ranges =
    +          static_cast<const RangePartitionSchemeHeader&>(rhs_partition_header).getPartitionRangeBoundaries();
    +
    +      return lhs_ranges == rhs_ranges;
    +    }
    +  }
    +
    +  return false;
    +}
    +
    +
    +// Note that this method will be deprecated once the partition scheme header
    +// supports multiple partition attributes.
    +size_t chooseBestRepartitionAttributeIndex(const CatalogRelationStatistics &stats,
    +                                           const vector<attribute_id> &join_attributes)
{
    +  size_t chose_attr_index = static_cast<size_t>(-1);
    +  size_t chose_attr_num_distinct_values = 0;
    +
    +  for (std::size_t i = 0; i < join_attributes.size(); ++i) {
    +    const attribute_id attr = join_attributes[i];
    +    if (stats.hasNumDistinctValues(attr) &&
    +        stats.getNumDistinctValues(attr) > chose_attr_num_distinct_values) {
    +      chose_attr_index = i;
    +      chose_attr_num_distinct_values = stats.getNumDistinctValues(attr);
    +    }
    +  }
    +
    +  return (chose_attr_index != static_cast<size_t>(-1)) ? chose_attr_index : 0;
    --- End diff --
    
    I am unable to understand the point of this function. Why do we need to find the "best
repartition attribute"? Assuming a join like ``R.a = S.b``, if ``R`` is partitioned on some
other attribute ``c``, we would like to repartition it based on ``a``, so the only choice
for an attribute on which we should perform the repartitioning is ``a``, isn't it? What's
the decision got do do with the CatalogRelation stats and the number of distinct values of
the attribute?


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