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/**
* Copyright (C) 2018-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 <vector>
#include "mongo/db/exec/plan_stage.h"
#include "mongo/db/jsobj.h"
#include "mongo/db/matcher/expression.h"
#include "mongo/db/record_id.h"
#include "mongo/stdx/unordered_map.h"
#include "mongo/stdx/unordered_set.h"
namespace mongo {
/**
* Reads from N children, each of which must have a valid RecordId. Uses a hash table to intersect
* the outputs of the N children based on their record ids, and outputs the intersection.
*
* Preconditions: Valid RecordId. More than one child.
*/
class AndHashStage final : public PlanStage {
public:
AndHashStage(OperationContext* opCtx, WorkingSet* ws);
/**
* For testing only. Allows tests to set memory usage threshold.
*/
AndHashStage(OperationContext* opCtx, WorkingSet* ws, size_t maxMemUsage);
void addChild(PlanStage* child);
/**
* Returns memory usage.
* For testing only.
*/
size_t getMemUsage() const;
StageState doWork(WorkingSetID* out) final;
bool isEOF() final;
StageType stageType() const final {
return STAGE_AND_HASH;
}
std::unique_ptr<PlanStageStats> getStats() final;
const SpecificStats* getSpecificStats() const final;
static const char* kStageType;
private:
static const size_t kLookAheadWorks;
StageState readFirstChild(WorkingSetID* out);
StageState hashOtherChildren(WorkingSetID* out);
StageState workChild(size_t childNo, WorkingSetID* out);
// Not owned by us.
WorkingSet* _ws;
// We want to see if any of our children are EOF immediately. This requires working them a
// few times to see if they hit EOF or if they produce a result. If they produce a result,
// we place that result here.
std::vector<WorkingSetID> _lookAheadResults;
// _dataMap is filled out by the first child and probed by subsequent children. This is the
// hash table that we create by intersecting _children and probe with the last child.
typedef stdx::unordered_map<RecordId, WorkingSetID, RecordId::Hasher> DataMap;
DataMap _dataMap;
// Keeps track of what elements from _dataMap subsequent children have seen.
// Only used while _hashingChildren.
typedef stdx::unordered_set<RecordId, RecordId::Hasher> SeenMap;
SeenMap _seenMap;
// True if we're still intersecting _children[0..._children.size()-1].
bool _hashingChildren;
// Which child are we currently working on?
size_t _currentChild;
// Stats
AndHashStats _specificStats;
// The usage in bytes of all buffered data that we're holding.
// Memory usage is calculated from keys held in _dataMap only.
// For simplicity, results in _lookAheadResults do not count towards the limit.
size_t _memUsage;
// Upper limit for buffered data memory usage.
// Defaults to 32 MB (See kMaxBytes in and_hash.cpp).
size_t _maxMemUsage;
};
} // namespace mongo
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