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/**
* Copyright (C) 2019-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#include "mongo/db/exec/sbe/expressions/expression.h"
#include "mongo/db/exec/sbe/stages/stages.h"
#include "mongo/db/exec/sbe/vm/vm.h"
namespace mongo::sbe {
enum class JoinType { Inner, Left, Right };
/**
* Implements a traditional nested loop join. For each advance from the 'outer' child, re-opens the
* 'inner' child and calls 'getNext()' on the inner child until EOF. The caller can optionally
* provide a join 'predicate' which is evaluated once per pair of outer and inner rows. If no
* predicate expression is provided, then the Cartesian product is produced.
*
* For symmetry with hash join, this is a binding reflector on the outer side. Nodes higher in the
* tree can only access those slots from the outer side that are named in 'outerProjects'. All slots
* from the inner side are visible.
*
* The 'outerCorrelated' slots are slots from the outer side which are made visible to the inner
* side.
*
* Debug string format:
*
* nlj [<outer projects>] [<outer correlated>] { predicate }
* left childStage
* right childStage
*/
class LoopJoinStage final : public PlanStage {
public:
// Legacy constructor.
LoopJoinStage(std::unique_ptr<PlanStage> outer,
std::unique_ptr<PlanStage> inner,
value::SlotVector outerProjects,
value::SlotVector outerCorrelated,
std::unique_ptr<EExpression> predicate,
PlanNodeId nodeId);
LoopJoinStage(std::unique_ptr<PlanStage> outer,
std::unique_ptr<PlanStage> inner,
value::SlotVector outerProjects,
value::SlotVector outerCorrelated,
value::SlotVector innerProjects,
std::unique_ptr<EExpression> predicate,
JoinType joinType,
PlanNodeId nodeId);
std::unique_ptr<PlanStage> clone() const final;
void prepare(CompileCtx& ctx) final;
value::SlotAccessor* getAccessor(CompileCtx& ctx, value::SlotId slot) final;
void open(bool reOpen) final;
PlanState getNext() final;
void close() final;
void doSaveState(bool relinquishCursor) final;
std::unique_ptr<PlanStageStats> getStats(bool includeDebugInfo) const final;
const SpecificStats* getSpecificStats() const final;
std::vector<DebugPrinter::Block> debugPrint() const final;
size_t estimateCompileTimeSize() const final;
private:
PlanState getNextOuterSide() {
_isReadingLeftSide = true;
auto ret = _children[0]->getNext();
_isReadingLeftSide = false;
return ret;
}
void openInner();
// Set of variables coming from the outer side. These are _not_ visible to the inner side,
// unless also added to '_outerCorrelated'.
const value::SlotVector _outerProjects;
// Set of correlated variables from the outer side that are visible on the inner side.
const value::SlotVector _outerCorrelated;
const value::SlotVector _innerProjects;
// Predicate to filter the joint set. If not set then the result is a cross product.
// Note: the predicate resolves the slots it's using through this stage's public accessors,
// meaning that if they are coming from the 'outer', they must be projected by the 'outer'.
const std::unique_ptr<EExpression> _predicate;
const JoinType _joinType;
vm::ByteCode _bytecode;
std::unique_ptr<vm::CodeFragment> _predicateCode;
// Switching between the input and Nothing/null for outer joins. Unused for inner joins.
value::SlotMap<value::SwitchAccessor> _outProjectAccessors;
// Defaults to Nothing. We have to explicitely reset to null if we want the null extenstion.
value::OwnedValueAccessor _constant;
// '_outerProjects' as a set (for faster checking of accessors, provided by the 'outer' child).
value::SlotSet _outerRefs;
PlanState _innerState{PlanState::IS_EOF};
bool _innerReturned{false};
bool _reOpenInner{false};
bool _outerGetNext{false};
LoopJoinStats _specificStats;
// Tracks whether or not we're reading from the left child or the right child.
// This is necessary for yielding.
bool _isReadingLeftSide = false;
};
} // namespace mongo::sbe
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