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#include <Common/Exception.h>
#include <Processors/QueryPlan/ReadFromMergeTree.h>
#include <Processors/QueryPlan/MergingAggregatedStep.h>
#include <Processors/QueryPlan/Optimizations/Optimizations.h>
#include <Processors/QueryPlan/Optimizations/QueryPlanOptimizationSettings.h>
#include <Processors/QueryPlan/UnionStep.h>
#include <stack>
namespace DB
{
namespace ErrorCodes
{
extern const int TOO_MANY_QUERY_PLAN_OPTIMIZATIONS;
extern const int PROJECTION_NOT_USED;
}
namespace QueryPlanOptimizations
{
void optimizeTreeFirstPass(const QueryPlanOptimizationSettings & settings, QueryPlan::Node & root, QueryPlan::Nodes & nodes)
{
if (!settings.optimize_plan)
return;
const auto & optimizations = getOptimizations();
struct Frame
{
QueryPlan::Node * node = nullptr;
/// If not zero, traverse only depth_limit layers of tree (if no other optimizations happen).
/// Otherwise, traverse all children.
size_t depth_limit = 0;
/// Next child to process.
size_t next_child = 0;
};
std::stack<Frame> stack;
stack.push({.node = &root});
size_t max_optimizations_to_apply = settings.max_optimizations_to_apply;
size_t total_applied_optimizations = 0;
while (!stack.empty())
{
auto & frame = stack.top();
/// If traverse_depth_limit == 0, then traverse without limit (first entrance)
/// If traverse_depth_limit > 1, then traverse with (limit - 1)
if (frame.depth_limit != 1)
{
/// Traverse all children first.
if (frame.next_child < frame.node->children.size())
{
stack.push(
{
.node = frame.node->children[frame.next_child],
.depth_limit = frame.depth_limit ? (frame.depth_limit - 1) : 0,
});
++frame.next_child;
continue;
}
}
size_t max_update_depth = 0;
/// Apply all optimizations.
for (const auto & optimization : optimizations)
{
if (!(settings.*(optimization.is_enabled)))
continue;
/// Just in case, skip optimization if it is not initialized.
if (!optimization.apply)
continue;
if (max_optimizations_to_apply && max_optimizations_to_apply < total_applied_optimizations)
throw Exception(ErrorCodes::TOO_MANY_QUERY_PLAN_OPTIMIZATIONS,
"Too many optimizations applied to query plan. Current limit {}",
max_optimizations_to_apply);
/// Try to apply optimization.
auto update_depth = optimization.apply(frame.node, nodes);
if (update_depth)
++total_applied_optimizations;
max_update_depth = std::max<size_t>(max_update_depth, update_depth);
}
/// Traverse `max_update_depth` layers of tree again.
if (max_update_depth)
{
frame.depth_limit = max_update_depth;
frame.next_child = 0;
continue;
}
/// Nothing was applied.
stack.pop();
}
}
void optimizeTreeSecondPass(const QueryPlanOptimizationSettings & optimization_settings, QueryPlan::Node & root, QueryPlan::Nodes & nodes)
{
size_t max_optimizations_to_apply = optimization_settings.max_optimizations_to_apply;
size_t num_applied_projection = 0;
bool has_reading_from_mt = false;
Stack stack;
stack.push_back({.node = &root});
while (!stack.empty())
{
/// NOTE: optimizePrewhere can modify the stack.
optimizePrewhere(stack, nodes);
optimizePrimaryKeyCondition(stack);
{
/// NOTE: frame cannot be safely used after stack was modified.
auto & frame = stack.back();
if (frame.next_child == 0)
{
has_reading_from_mt |= typeid_cast<const ReadFromMergeTree *>(frame.node->step.get()) != nullptr;
if (optimization_settings.read_in_order)
optimizeReadInOrder(*frame.node, nodes);
/// Projection optimization relies on PK optimization
if (optimization_settings.optimize_projection)
num_applied_projection
+= optimizeUseAggregateProjections(*frame.node, nodes, optimization_settings.optimize_use_implicit_projections);
if (optimization_settings.aggregation_in_order)
optimizeAggregationInOrder(*frame.node, nodes);
if (optimization_settings.distinct_in_order)
tryDistinctReadInOrder(frame.node);
}
/// Traverse all children first.
if (frame.next_child < frame.node->children.size())
{
auto next_frame = Frame{.node = frame.node->children[frame.next_child]};
++frame.next_child;
stack.push_back(next_frame);
continue;
}
}
if (optimization_settings.optimize_projection)
{
/// Projection optimization relies on PK optimization
if (optimizeUseNormalProjections(stack, nodes))
{
++num_applied_projection;
if (max_optimizations_to_apply && max_optimizations_to_apply < num_applied_projection)
throw Exception(ErrorCodes::TOO_MANY_QUERY_PLAN_OPTIMIZATIONS,
"Too many projection optimizations applied to query plan. Current limit {}",
max_optimizations_to_apply);
/// Stack is updated after this optimization and frame is not valid anymore.
/// Try to apply optimizations again to newly added plan steps.
--stack.back().next_child;
continue;
}
}
enableMemoryBoundMerging(*stack.back().node, nodes);
stack.pop_back();
}
if (optimization_settings.force_use_projection && has_reading_from_mt && num_applied_projection == 0)
throw Exception(
ErrorCodes::PROJECTION_NOT_USED,
"No projection is used when optimize_use_projections = 1 and force_optimize_projection = 1");
}
void optimizeTreeThirdPass(QueryPlan & plan, QueryPlan::Node & root, QueryPlan::Nodes & nodes)
{
Stack stack;
stack.push_back({.node = &root});
while (!stack.empty())
{
/// NOTE: frame cannot be safely used after stack was modified.
auto & frame = stack.back();
/// Traverse all children first.
if (frame.next_child < frame.node->children.size())
{
auto next_frame = Frame{.node = frame.node->children[frame.next_child]};
++frame.next_child;
stack.push_back(next_frame);
continue;
}
if (auto * source_step_with_filter = dynamic_cast<SourceStepWithFilter *>(frame.node->step.get()))
{
source_step_with_filter->applyFilters();
}
addPlansForSets(plan, *frame.node, nodes);
stack.pop_back();
}
}
}
}
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