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/**
* Copyright (C) 2023-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/plan_stage.h"
#include "mongo/db/exec/plan_stats.h"
#include "mongo/db/pipeline/memory_usage_tracker.h"
#include "mongo/db/sorter/sorter.h"
namespace mongo {
/**
* Spools the inputs received from the child in a buffer. This is an eager spool: initially, on each
* call to doWork() it reads as much as it can from its child (propagating yields and NEED_TIME) and
* caches it in a buffer. Once the input has been exhausted, calls to doWork() return the cached
* results.
*
* Note that to reduce memory and disk usage, the spool only caches RecordIds. Callers must fetch
* the corresponding documents as needed.
*/
class SpoolStage final : public PlanStage {
public:
static const char* kStageType;
SpoolStage(ExpressionContext* expCtx, WorkingSet* ws, std::unique_ptr<PlanStage> child);
StageType stageType() const {
return STAGE_SPOOL;
}
bool isEOF() final;
std::unique_ptr<PlanStageStats> getStats();
const SpecificStats* getSpecificStats() const {
return &_specificStats;
}
protected:
PlanStage::StageState doWork(WorkingSetID* id);
private:
void spill();
WorkingSet* _ws;
SpoolStats _specificStats;
// Next index to consume from the buffer. If < 0, the buffer is not yet fully populated from the
// child.
int _nextIndex = -1;
// Buffer caching spooled results in-memory.
std::vector<RecordId> _buffer;
// Machinery for spilling to disk.
MemoryUsageTracker _memTracker;
std::unique_ptr<SorterFileStats> _spillStats;
std::shared_ptr<Sorter<RecordId, NullValue>::File> _file;
// Iterators over the file that has been spilled to disk. These must be exhausted in addition to
// '_buffer' when returning results.
std::deque<std::shared_ptr<Sorter<RecordId, NullValue>::Iterator>> _spillFileIters;
};
} // namespace mongo
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