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89 lines
2.8 KiB
C++
89 lines
2.8 KiB
C++
#pragma once
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#include <memory>
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#include <unordered_map>
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#include <set>
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#include <DB/Core/Block.h>
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namespace Poco { class Logger; }
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namespace DB
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{
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class IAST;
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using ASTPtr = std::shared_ptr<IAST>;
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class ASTSelectQuery;
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class ASTFunction;
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class MergeTreeData;
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using IdentifierNameSet = std::set<std::string>;
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/** Identifies WHERE expressions that can be placed in PREWHERE by calculating respective
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* sizes of columns used in particular expression and identifying "good" conditions of
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* form "column_name = constant", where "constant" is outside some `threshold` specified in advance.
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*
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* If there are "good" conditions present in WHERE, the one with minimal summary column size is
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* transferred to PREWHERE.
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* Otherwise any condition with minimal summary column size can be transferred to PREWHERE, if only
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* its relative size (summary column size divided by query column size) is less than `max_columns_relative_size`.
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*/
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class MergeTreeWhereOptimizer
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{
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public:
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MergeTreeWhereOptimizer(const MergeTreeWhereOptimizer&) = delete;
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MergeTreeWhereOptimizer& operator=(const MergeTreeWhereOptimizer&) = delete;
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MergeTreeWhereOptimizer(
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ASTPtr & query, const Context & context, const MergeTreeData & data, const Names & column_names,
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Poco::Logger * log);
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private:
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void optimize(ASTSelectQuery & select) const;
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void calculateColumnSizes(const MergeTreeData & data, const Names & column_names);
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void optimizeConjunction(ASTSelectQuery & select, ASTFunction * const fun) const;
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void optimizeArbitrary(ASTSelectQuery & select) const;
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std::size_t getIdentifiersColumnSize(const IdentifierNameSet & identifiers) const;
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bool isConditionGood(const IAST * condition) const;
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static void collectIdentifiersNoSubqueries(const IAST * const ast, IdentifierNameSet & set);
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bool hasPrimaryKeyAtoms(const IAST * ast) const;
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bool isPrimaryKeyAtom(const IAST * const ast) const;
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bool isConstant(const ASTPtr & expr) const;
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bool isSubsetOfTableColumns(const IdentifierNameSet & identifiers) const;
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/** ARRAY JOIN'ed columns as well as arrayJoin() result cannot be used in PREWHERE, therefore expressions
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* containing said columns should not be moved to PREWHERE at all.
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* We assume all AS aliases have been expanded prior to using this class
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*
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* Also, disallow moving expressions with GLOBAL [NOT] IN.
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*/
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bool cannotBeMoved(const IAST * ptr) const;
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void determineArrayJoinedNames(ASTSelectQuery & select);
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using string_set_t = std::unordered_set<std::string>;
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const string_set_t primary_key_columns;
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const string_set_t table_columns;
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const Block block_with_constants;
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Poco::Logger * log;
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std::unordered_map<std::string, std::size_t> column_sizes{};
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std::size_t total_column_size{};
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NameSet array_joined_names;
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};
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}
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