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Fix review comments

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This commit is contained in:
Igor Nikonov 2023-02-02 11:46:13 +00:00
parent 996b833faa
commit 32ab4dc693
1 changed files with 97 additions and 81 deletions
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178
src/Processors/QueryPlan/Optimizations/removeRedundantDistinct.cpp
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@ -36,97 +36,113 @@ namespace
}
return non_const_columns;
}
bool canRemoveDistinct(const QueryPlan::Node * distinct_node)
{
const DistinctStep * distinct_step = typeid_cast<DistinctStep *>(distinct_node->step.get());
chassert(distinct_step);
std::vector<ActionsDAGPtr> dag_stack;
const DistinctStep * inner_distinct_step = nullptr;
const QueryPlan::Node * node = distinct_node;
while (!node->children.empty())
{
const IQueryPlanStep * current_step = node->step.get();
/// don't try to remove DISTINCT after union or join
if (typeid_cast<const UnionStep *>(current_step) || typeid_cast<const JoinStep *>(current_step)
|| typeid_cast<const IntersectOrExceptStep *>(current_step))
break;
if (const auto * const expr = typeid_cast<const ExpressionStep *>(current_step); expr)
dag_stack.push_back(expr->getExpression());
if (const auto * const filter = typeid_cast<const FilterStep *>(current_step); filter)
dag_stack.push_back(filter->getExpression());
node = node->children.front();
inner_distinct_step = typeid_cast<DistinctStep *>(node->step.get());
if (inner_distinct_step)
break;
}
if (!inner_distinct_step)
return false;
/// possible cases (outer distinct -> inner distinct):
/// final -> preliminary => do nothing
/// preliminary -> final => try remove preliminary
/// final -> final => try remove final
/// preliminary -> preliminary => logical error?
if (inner_distinct_step->isPreliminary())
return false;
const auto distinct_columns = getDistinctColumns(distinct_step);
auto inner_distinct_columns = getDistinctColumns(inner_distinct_step);
if (distinct_columns.size() != inner_distinct_columns.size())
return false;
ActionsDAGPtr path_actions;
if (!dag_stack.empty())
{
/// build actions DAG to find original column names
path_actions = dag_stack.back();
dag_stack.pop_back();
while (!dag_stack.empty())
{
ActionsDAGPtr clone = dag_stack.back()->clone();
dag_stack.pop_back();
path_actions->mergeInplace(std::move(*clone));
}
logActionsDAG("merged DAG:\n{}", path_actions);
/// compare columns of two DISTINCTs
for (const auto & column : distinct_columns)
{
const auto * alias_node = path_actions->getOriginalNodeForOutputAlias(String(column));
if (!alias_node)
return false;
auto it = inner_distinct_columns.find(alias_node->result_name);
if (it == inner_distinct_columns.end())
return false;
inner_distinct_columns.erase(it);
}
}
else
{
if (distinct_columns != inner_distinct_columns)
return false;
}
return true;
}
}
///
/// DISTINCT is redundant if DISTINCT on the same columns was executed before
/// Trivial example: SELECT DISTINCT * FROM (SELECT DISTINCT * FROM numbers(3))
///
size_t tryRemoveRedundantDistinct(QueryPlan::Node * parent_node, QueryPlan::Nodes & /* nodes*/)
{
if (parent_node->children.empty())
return 0;
/// check if it is preliminary distinct node
QueryPlan::Node * distinct_node = parent_node->children.front();
DistinctStep * distinct_step = typeid_cast<DistinctStep *>(distinct_node->step.get());
if (!distinct_step)
return 0;
std::vector<ActionsDAGPtr> dag_stack;
const DistinctStep * inner_distinct_step = nullptr;
QueryPlan::Node * node = distinct_node;
while (!node->children.empty())
bool applied = false;
for (const auto * node : parent_node->children)
{
const IQueryPlanStep * current_step = node->step.get();
/// check if it is distinct node
const DistinctStep * distinct_step = typeid_cast<DistinctStep *>(node->step.get());
if (!distinct_step)
continue;
/// don't try to remove DISTINCT after union or join
if (typeid_cast<const UnionStep *>(current_step) || typeid_cast<const JoinStep *>(current_step)
|| typeid_cast<const IntersectOrExceptStep *>(current_step))
break;
if (const auto * const expr = typeid_cast<const ExpressionStep *>(current_step); expr)
dag_stack.push_back(expr->getExpression());
if (const auto * const filter = typeid_cast<const FilterStep *>(current_step); filter)
dag_stack.push_back(filter->getExpression());
node = node->children.front();
inner_distinct_step = typeid_cast<DistinctStep *>(node->step.get());
if (inner_distinct_step)
break;
}
if (!inner_distinct_step)
return 0;
/// possible cases (outer distinct -> inner distinct):
/// final -> preliminary => do nothing
/// preliminary -> final => try remove preliminary
/// final -> final => try remove final
/// preliminary -> preliminary => logical error?
if (inner_distinct_step->isPreliminary())
return 0;
const auto distinct_columns = getDistinctColumns(distinct_step);
auto inner_distinct_columns = getDistinctColumns(inner_distinct_step);
if (distinct_columns.size() != inner_distinct_columns.size())
return 0;
ActionsDAGPtr path_actions;
if (!dag_stack.empty())
{
/// build actions DAG to find original column names
path_actions = dag_stack.back();
dag_stack.pop_back();
while (!dag_stack.empty())
if (canRemoveDistinct(node))
{
ActionsDAGPtr clone = dag_stack.back()->clone();
dag_stack.pop_back();
path_actions->mergeInplace(std::move(*clone));
}
logActionsDAG("merged DAG:\n{}", path_actions);
/// compare columns of two DISTINCTs
for (const auto & column : distinct_columns)
{
const auto * alias_node = path_actions->getOriginalNodeForOutputAlias(String(column));
if (!alias_node)
return 0;
auto it = inner_distinct_columns.find(alias_node->result_name);
if (it == inner_distinct_columns.end())
return 0;
inner_distinct_columns.erase(it);
/// remove current distinct
chassert(!node->children.empty());
parent_node->children[0] = node->children.front();
applied = true;
}
}
else
{
if (distinct_columns != inner_distinct_columns)
return 0;
}
/// remove current distinct
chassert(!distinct_node->children.empty());
parent_node->children[0] = distinct_node->children.front();
return 1;
return applied;
}
}