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Refactor DAG splitting into steps
This commit is contained in:
Alexander Gololobov
parent
943f2ea212
commit
3ad0683de9
@ -17,6 +17,7 @@
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/// For CAST to bool
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#include <Functions/CastOverloadResolver.h>
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#include <Functions/FunctionsLogical.h>
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#include <Planner/PlannerActionsVisitor.h>
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#include <city.h>
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@ -108,6 +109,255 @@ static const ActionsDAG::Node & addCast(ActionsDAGPtr dag, const ActionsDAG::Nod
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return dag->addFunction(func_builder_cast, std::move(children), new_name);
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};
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struct NodeInfo
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{
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NameSet required_columns;
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};
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void fillRequiredColumns(const ActionsDAG::Node * node, std::unordered_map<const ActionsDAG::Node *, NodeInfo> & nodes_info)
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{
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if (nodes_info.contains(node))
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return;
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auto & node_info = nodes_info[node];
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if (node->type == ActionsDAG::ActionType::INPUT)
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{
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node_info.required_columns.insert(node->result_name);
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return;
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}
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for (const auto & child : node->children)
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{
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fillRequiredColumns(child, nodes_info);
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const auto & child_info = nodes_info[child];
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node_info.required_columns.insert(child_info.required_columns.begin(), child_info.required_columns.end());
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}
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}
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struct DAGNodeRef
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{
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ActionsDAGPtr dag;
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const ActionsDAG::Node * node;
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};
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using OriginalToNewNodeMap = std::unordered_map<const ActionsDAG::Node *, DAGNodeRef>;
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const ActionsDAG::Node & addClonedDAGToDAG(const ActionsDAG::Node * original_dag_node, ActionsDAGPtr new_dag, OriginalToNewNodeMap & node_remap)
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{
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if (node_remap.contains(original_dag_node))
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{
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/// If the node is already in the new DAG, return it
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const auto & node_ref = node_remap.at(original_dag_node);
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if (node_ref.dag == new_dag)
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return *node_ref.node;
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/// If the node is known from the previous steps, add it as an input
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node_ref.dag->addOrReplaceInOutputs(*node_ref.node);
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const auto & new_node = new_dag->addInput(node_ref.node->result_name, node_ref.node->result_type);
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node_remap[original_dag_node] = {new_dag, &new_node}; /// TODO: here we update the node reference. Is ti always correct?
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return new_node;
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}
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/// If the node is an input, add it as an input
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if (original_dag_node->type == ActionsDAG::ActionType::INPUT)
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{
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const auto & new_node = new_dag->addInput(original_dag_node->result_name, original_dag_node->result_type);
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node_remap[original_dag_node] = {new_dag, &new_node};
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return new_node;
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}
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/// If the node is a column, add it as an input
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if (original_dag_node->type == ActionsDAG::ActionType::COLUMN)
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{
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const auto & new_node = new_dag->addColumn(
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ColumnWithTypeAndName(original_dag_node->column, original_dag_node->result_type, original_dag_node->result_name));
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node_remap[original_dag_node] = {new_dag, &new_node};
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return new_node;
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}
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/// TODO: Alias node?
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/// If the node is a function, add it as a function and add its children
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if (original_dag_node->type == ActionsDAG::ActionType::FUNCTION)
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{
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ActionsDAG::NodeRawConstPtrs new_children;
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for (const auto & child : original_dag_node->children)
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{
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const auto & new_child = addClonedDAGToDAG(child, new_dag, node_remap);
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new_children.push_back(&new_child);
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}
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const auto & new_node = new_dag->addFunction(original_dag_node->function_base, new_children, original_dag_node->result_name);
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node_remap[original_dag_node] = {new_dag, &new_node};
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return new_node;
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}
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throw Exception(ErrorCodes::LOGICAL_ERROR, "Unexpected node type in PREWHERE actions: {}", original_dag_node->type);
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}
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bool tryBuildPrewhereSteps(PrewhereInfoPtr prewhere_info, const ExpressionActionsSettings & actions_settings, PrewhereExprInfo & prewhere)
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{
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/// We want to build a sequence of steps that will compute parts of the prewhere condition.
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/// Each step reads some new columns and computes some new expressions and a filter condition.
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/// The last step computes the final filter condition and the remaining expressions that are required for the main query.
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/// The steps are built in the following way:
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/// 1. List all condition nodes that are combined with AND into PREWHERE condition
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/// 2. Collect the set of columns that are used in the condition
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/// 3. Sort condition nodes by the number of columns used in them and the overall size of those columns
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/// 4. Group conditions with the same set of columns into a single read/compute step
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/// 5. Build DAGs for each step:
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/// - DFS from the condition root node:
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/// - If the node was not computed yet, add it to the DAG and traverse its children
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/// - If the node was already computed by one of the previous steps, add it as output for that step and as input for the current step
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/// - If the node was already computed by the current step just stop traversing
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/// 6. Find all outputs of the original DAG
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/// 7. Find all outputs that were computed in the already built DAGs, mark these nodes as outputs in the steps where they were computed
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/// 8. Add computation of the remaining outputs to the last step with the procedure similar to 4
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if (!prewhere_info || !prewhere_info->prewhere_actions)
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return true;
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/// 1. List all condition nodes that are combined with AND into PREWHERE condition
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const auto & condition_root = prewhere_info->prewhere_actions->findInOutputs(prewhere_info->prewhere_column_name);
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const bool is_conjunction = (condition_root.type == ActionsDAG::ActionType::FUNCTION && condition_root.function_base->getName() == "and");
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if (!is_conjunction)
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return false;
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auto condition_nodes = condition_root.children;
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/// 2. Collect the set of columns that are used in the condition
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std::unordered_map<const ActionsDAG::Node *, NodeInfo> nodes_info;
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for (const auto & node : condition_nodes)
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{
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fillRequiredColumns(node, nodes_info);
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}
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/// 3. Sort condition nodes by the number of columns used in them and the overall size of those columns
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/// TODO: not sorting for now because the conditions are already sorted by Where Optimizer
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/// 4. Group conditions with the same set of columns into a single read/compute step
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std::vector<std::vector<const ActionsDAG::Node *>> condition_groups;
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for (const auto & node : condition_nodes)
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{
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const auto & node_info = nodes_info[node];
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if (!condition_groups.empty() && nodes_info[condition_groups.back().back()].required_columns == node_info.required_columns)
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condition_groups.back().push_back(node); /// Add to the last group
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else
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condition_groups.push_back({node}); /// Start new group
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}
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/// 5. Build DAGs for each step
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struct Step
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{
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ActionsDAGPtr actions;
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String column_name;
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};
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std::vector<Step> steps;
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OriginalToNewNodeMap node_remap;
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for (const auto & condition_group : condition_groups)
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{
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// std::cerr
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// << "Conditions: [";
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//
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// for (const auto & condition : condition_group)
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// std::cerr << " \"" << condition->result_name;
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//
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// std::cerr << "\" ] Columns: " << boost::algorithm::join(nodes_info[condition_group.front()].required_columns, " ")
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// << std::endl;
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ActionsDAGPtr step_dag = std::make_shared<ActionsDAG>();
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String result_name;
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std::vector<const ActionsDAG::Node *> new_condition_nodes;
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for (const auto * node : condition_group)
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{
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const auto & node_in_new_dag = addClonedDAGToDAG(node, step_dag, node_remap);
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new_condition_nodes.push_back(&node_in_new_dag);
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}
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if (new_condition_nodes.size() > 1)
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{
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/// Add AND function to combine the conditions
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FunctionOverloadResolverPtr func_builder_and = std::make_unique<FunctionToOverloadResolverAdaptor>(std::make_shared<FunctionAnd>());
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const auto & and_function_node = step_dag->addFunction(func_builder_and, new_condition_nodes, "");
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step_dag->addOrReplaceInOutputs(and_function_node);
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result_name = and_function_node.result_name;
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}
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else
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{
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const auto & result_node = *new_condition_nodes.front();
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/// Add cast to UInt8 if needed
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if (result_node.result_type->getTypeId() == TypeIndex::UInt8)
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{
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step_dag->addOrReplaceInOutputs(result_node);
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result_name = result_node.result_name;
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}
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else
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{
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const auto & cast_node = addCast(step_dag, result_node, "UInt8");
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step_dag->addOrReplaceInOutputs(cast_node);
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result_name = cast_node.result_name;
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}
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}
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// std::cerr << "Step DAG:\n" << step_dag->dumpDAG() << std::endl;
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steps.push_back({step_dag, result_name});
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}
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/// 6. Find all outputs of the original DAG
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auto original_outputs = prewhere_info->prewhere_actions->getOutputs();
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/// 7. Find all outputs that were computed in the already built DAGs, mark these nodes as outputs in the steps where they were computed
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/// 8. Add computation of the remaining outputs to the last step with the procedure similar to 4
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for (const auto * output : original_outputs)
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{
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// std::cerr << "Original output: " << output->result_name << std::endl;
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if (node_remap.contains(output))
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{
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const auto & new_node_info = node_remap[output];
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new_node_info.dag->addOrReplaceInOutputs(*new_node_info.node);
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}
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else if (output->result_name == prewhere_info->prewhere_column_name)
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{
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/// Special case for final PREWHERE column:
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/// "Rename" the last step result to the combined PREWHERE column name, because in fact it will be AND of all step results
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const auto & prewhere_result_node = addCast(
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steps.back().actions,
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steps.back().actions->findInOutputs(steps.back().column_name),
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output->result_type->getName(),
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prewhere_info->prewhere_column_name);
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steps.back().actions->addOrReplaceInOutputs(prewhere_result_node);
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}
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else
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{
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const auto & node_in_new_dag = addClonedDAGToDAG(output, steps.back().actions, node_remap);
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steps.back().actions->addOrReplaceInOutputs(node_in_new_dag);
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}
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}
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/// 9. Build PrewhereExprInfo
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{
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for (const auto & step : steps)
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{
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// std::cerr << "Step DAG:\n" << step.actions->dumpDAG() << std::endl;
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prewhere.steps.push_back(
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{
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.actions = std::make_shared<ExpressionActions>(step.actions, actions_settings),
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.column_name = step.column_name,
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.remove_column = true,
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.need_filter = false,
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});
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}
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prewhere.steps.back().remove_column = prewhere_info->remove_prewhere_column;
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prewhere.steps.back().need_filter = prewhere_info->need_filter;
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}
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return true;
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}
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std::unique_ptr<PrewhereExprInfo> IMergeTreeSelectAlgorithm::getPrewhereActions(PrewhereInfoPtr prewhere_info, const ExpressionActionsSettings & actions_settings, bool enable_multiple_prewhere_read_steps)
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{
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std::unique_ptr<PrewhereExprInfo> prewhere_actions;
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@ -130,6 +380,22 @@ std::unique_ptr<PrewhereExprInfo> IMergeTreeSelectAlgorithm::getPrewhereActions(
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// std::cerr << "ORIGINAL PREWHERE:\n" << prewhere_info->prewhere_actions->dumpDAG() << std::endl;
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#if 1
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if (!enable_multiple_prewhere_read_steps || !tryBuildPrewhereSteps(prewhere_info, actions_settings, *prewhere_actions))
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{
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PrewhereExprStep prewhere_step
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{
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.actions = std::make_shared<ExpressionActions>(prewhere_info->prewhere_actions, actions_settings),
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.column_name = prewhere_info->prewhere_column_name,
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.remove_column = prewhere_info->remove_prewhere_column,
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.need_filter = prewhere_info->need_filter
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};
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prewhere_actions->steps.emplace_back(std::move(prewhere_step));
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}
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#else
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struct Step
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{
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ActionsDAGPtr actions;
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@ -243,6 +509,7 @@ std::unique_ptr<PrewhereExprInfo> IMergeTreeSelectAlgorithm::getPrewhereActions(
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prewhere_actions->steps.emplace_back(std::move(prewhere_step));
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}
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#endif
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}
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return prewhere_actions;
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