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110 lines
3.3 KiB
C++
110 lines
3.3 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 <boost/noncopyable.hpp>
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#include <Core/Block.h>
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#include <Storages/SelectQueryInfo.h>
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namespace Poco { class Logger; }
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namespace DB
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{
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class ASTSelectQuery;
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class ASTFunction;
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class MergeTreeData;
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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 transferred to PREWHERE.
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* Otherwise any condition with minimal summary column size can be transferred to PREWHERE.
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*/
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class MergeTreeWhereOptimizer : private boost::noncopyable
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{
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public:
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MergeTreeWhereOptimizer(
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SelectQueryInfo & query_info,
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const Context & context,
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const MergeTreeData & data,
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const Names & queried_columns_,
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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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struct Condition
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{
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ASTPtr node;
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UInt64 columns_size = 0;
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NameSet identifiers;
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bool viable = false;
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bool good = false;
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auto tuple() const
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{
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return std::make_tuple(!viable, !good, columns_size);
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}
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/// Is condition a better candidate for moving to PREWHERE?
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bool operator< (const Condition & rhs) const
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{
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return tuple() < rhs.tuple();
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}
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};
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using Conditions = std::list<Condition>;
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void analyzeImpl(Conditions & res, const ASTPtr & node) const;
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/// Transform conjunctions chain in WHERE expression to Conditions list.
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Conditions analyze(const ASTPtr & expression) const;
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/// Transform Conditions list to WHERE or PREWHERE expression.
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static ASTPtr reconstruct(const Conditions & conditions);
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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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UInt64 getIdentifiersColumnSize(const NameSet & identifiers) const;
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bool hasPrimaryKeyAtoms(const ASTPtr & ast) const;
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bool isPrimaryKeyAtom(const ASTPtr & ast) const;
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bool isConstant(const ASTPtr & expr) const;
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bool isSubsetOfTableColumns(const NameSet & 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 ASTPtr & ptr) const;
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void determineArrayJoinedNames(ASTSelectQuery & select);
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using StringSet = std::unordered_set<std::string>;
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String first_primary_key_column;
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const StringSet table_columns;
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const Names queried_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, UInt64> column_sizes;
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UInt64 total_size_of_queried_columns = 0;
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NameSet array_joined_names;
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};
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}
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