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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 <set>
#include <vector>
#include "mongo/db/exec/plan_stage.h"
#include "mongo/db/exec/sort_key_generator.h"
#include "mongo/db/exec/working_set.h"
#include "mongo/db/jsobj.h"
#include "mongo/db/query/index_bounds.h"
#include "mongo/db/record_id.h"
#include "mongo/stdx/unordered_map.h"
namespace mongo {
class BtreeKeyGenerator;
// Parameters that must be provided to a SortStage
class SortStageParams {
public:
SortStageParams() = default;
// How we're sorting.
BSONObj pattern;
// Equal to 0 for no limit.
size_t limit = 0;
};
/**
* Sorts the input received from the child according to the sort pattern provided.
*
* Preconditions:
* -- For each field in 'pattern', all inputs in the child must handle a getFieldDotted for that
* field.
* -- All WSMs produced by the child stage must have the sort key available as WSM computed data.
*/
class SortStage final : public PlanStage {
public:
SortStage(OperationContext* opCtx,
const SortStageParams& params,
WorkingSet* ws,
PlanStage* child);
~SortStage();
bool isEOF() final;
StageState doWork(WorkingSetID* out) final;
StageType stageType() const final {
return STAGE_SORT;
}
std::unique_ptr<PlanStageStats> getStats();
const SpecificStats* getSpecificStats() const final;
static const char* kStageType;
private:
//
// Query Stage
//
// Not owned by us.
WorkingSet* _ws;
// The raw sort _pattern as expressed by the user
BSONObj _pattern;
// Equal to 0 for no limit.
size_t _limit;
//
// Data storage
//
// Have we sorted our data? If so, we can access _resultIterator. If not,
// we're still populating _data.
bool _sorted;
// Collection of working set members to sort with their respective sort key.
struct SortableDataItem {
WorkingSetID wsid;
BSONObj sortKey;
// Since we must replicate the behavior of a covered sort as much as possible we use the
// RecordId to break sortKey ties.
// See sorta.js.
RecordId recordId;
};
// Comparison object for data buffers (vector and set). Items are compared on (sortKey, loc).
// This is also how the items are ordered in the indices. Keys are compared using
// BSONObj::woCompare() with RecordId as a tie-breaker.
//
// We are comparing keys generated by the SortKeyGenerator, which are already ordered with
// respect the collation. Therefore, we explicitly avoid comparing using a collator here.
struct WorkingSetComparator {
explicit WorkingSetComparator(BSONObj p);
bool operator()(const SortableDataItem& lhs, const SortableDataItem& rhs) const;
BSONObj pattern;
};
/**
* Inserts one item into data buffer (vector or set).
* If limit is exceeded, remove item with lowest key.
*/
void addToBuffer(const SortableDataItem& item);
/**
* Sorts data buffer.
* Assumes no more items will be added to buffer.
* If data is stored in set, copy set
* contents to vector and clear set.
*/
void sortBuffer();
// Comparator for data buffer
// Initialization follows sort key generator
std::unique_ptr<WorkingSetComparator> _sortKeyComparator;
// The data we buffer and sort.
// _data will contain sorted data when all data is gathered
// and sorted.
// When _limit is greater than 1 and not all data has been gathered from child stage,
// _dataSet is used instead to maintain an ordered set of the incomplete data set.
// When the data set is complete, we copy the items from _dataSet to _data which will
// be used to provide the results of this stage through _resultIterator.
std::vector<SortableDataItem> _data;
typedef std::set<SortableDataItem, WorkingSetComparator> SortableDataItemSet;
std::unique_ptr<SortableDataItemSet> _dataSet;
// Iterates through _data post-sort returning it.
std::vector<SortableDataItem>::iterator _resultIterator;
SortStats _specificStats;
// The usage in bytes of all buffered data that we're sorting.
size_t _memUsage;
};
} // namespace mongo
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