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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 <memory>
#include <queue>
#include <vector>
#include "mongo/base/status_with.h"
#include "mongo/base/string_data.h"
#include "mongo/db/catalog/collection.h"
#include "mongo/db/exec/plan_stats.h"
#include "mongo/db/exec/requires_collection_stage.h"
#include "mongo/db/exec/working_set.h"
#include "mongo/db/jsobj.h"
#include "mongo/db/record_id.h"
#include "mongo/stdx/unordered_map.h"
namespace mongo {
/**
* An abstract stage which uses a progressive sort to return results sorted by distance. This
* is useful when we do not have a full ordering computed over the distance metric and don't
* want to generate one.
*
* Some parts of the geoNear implementation depend on the type of index being used, so
* subclasses need to implement these three functions:
*
* - initialize() - Prepares the stage to begin the geoNear search. Must return IS_EOF iff the
* stage is prepared to begin buffering documents.
* - nextInterval() - Must return the bounds of the next interval with a PlanStage that will find
* all of the results in this interval that have not already been buffered in
* previous intervals.
* - computeDistance() - Must return the distance from a document to the centroid of search using
* the correct metric (spherical/flat, radians/meters).
*
* For example - given a distance search over documents with distances from [0 -> 10], the child
* stage might break up the search into intervals [0->5),[5,7),[7->10].
*
* Each interval requires a PlanStage which returns all of the results in the interval that have
* not been buffered in a previous interval. Results in each interval are buffered fully before
* being returned to ensure that ordering is preserved. Results that are in the cover, but outside
* the outer bounds of the current interval will remain buffered to be returned in subsequent
* search intervals.
*
* For efficient search, the child stage should not return too many results outside the interval,
* but correctness only depends on all the results in the interval being buffered before any are
* returned. As an example, a PlanStage for the interval [0->5) might just be a full collection
* scan - this will always buffer every result in the interval, but is slow. If there is an index
* available, an IndexScan stage might also return all documents with distance [0->5) but
* would be much faster.
*
* Also for efficient search, the intervals should not be too large or too small - though again
* correctness does not depend on interval size.
*
* The child stage may return duplicate documents, so it is the responsibility of NearStage to
* deduplicate. Every document in _resultBuffer is kept track of in _seenDocuments. When a document
* is returned, it is removed from _seenDocuments.
*
* TODO: Right now the interface allows the nextCovering() to be adaptive, but doesn't allow
* aborting and shrinking a covered range being buffered if we guess wrong.
*/
class NearStage : public RequiresCollectionStage {
public:
struct CoveredInterval;
~NearStage();
bool isEOF() final;
StageState doWork(WorkingSetID* out) final;
StageType stageType() const final;
std::unique_ptr<PlanStageStats> getStats() final;
const SpecificStats* getSpecificStats() const final;
protected:
/**
* Subclasses of NearStage must provide basics + a stats object which gets owned here.
*/
NearStage(OperationContext* opCtx,
const char* typeName,
StageType type,
WorkingSet* workingSet,
const Collection* collection);
//
// Methods implemented for specific search functionality
//
/**
* Constructs the next covering over the next interval to buffer results from, or NULL
* if the full range has been searched. Use the provided working set as the working
* set for the covering stage if required.
*
* Returns !OK on failure to create next stage.
*/
virtual StatusWith<CoveredInterval*> nextInterval(OperationContext* opCtx,
WorkingSet* workingSet,
const Collection* collection) = 0;
/**
* Computes the distance value for the given member data, or -1 if the member should not be
* returned in the sorted results.
*
* Returns !OK on invalid member data.
*/
virtual StatusWith<double> computeDistance(WorkingSetMember* member) = 0;
/*
* Initialize near stage before buffering the data.
* Return IS_EOF if subclass finishes the initialization.
* Return NEED_TIME if we need more time.
* Return errors if an error occurs.
* Can't return ADVANCED.
*/
virtual StageState initialize(OperationContext* opCtx,
WorkingSet* workingSet,
WorkingSetID* out) = 0;
void saveState(RequiresCollTag) final {}
void restoreState(RequiresCollTag) final {}
// Filled in by subclasses.
NearStats _specificStats;
private:
//
// Generic methods for progressive search functionality
//
StageState initNext(WorkingSetID* out);
StageState bufferNext(WorkingSetID* toReturn, Status* error);
StageState advanceNext(WorkingSetID* toReturn);
//
// Generic state for progressive near search
//
WorkingSet* const _workingSet;
// A progressive search works in stages of buffering and then advancing
enum SearchState {
SearchState_Initializing,
SearchState_Buffering,
SearchState_Advancing,
SearchState_Finished
} _searchState;
// Tracks RecordIds from the child stage to do our own deduping.
stdx::unordered_map<RecordId, WorkingSetID, RecordId::Hasher> _seenDocuments;
// Stats for the stage covering this interval
// This is owned by _specificStats
IntervalStats* _nextIntervalStats;
// Sorted buffered results to be returned - the current interval
struct SearchResult;
std::priority_queue<SearchResult> _resultBuffer;
// Stats
const StageType _stageType;
// The current stage from which this stage should buffer results
// Pointer to the last interval in _childrenIntervals. Owned by _childrenIntervals.
CoveredInterval* _nextInterval;
// All children CoveredIntervals and the sub-stages owned by them.
//
// All children intervals except the last active one are only used by getStats(),
// because they are all EOF.
std::vector<std::unique_ptr<CoveredInterval>> _childrenIntervals;
};
/**
* A covered interval over which a portion of a near search can be run.
*/
struct NearStage::CoveredInterval {
CoveredInterval(PlanStage* covering, double minDistance, double maxDistance, bool inclusiveMax);
PlanStage* const covering; // Owned in PlanStage::_children.
const double minDistance;
const double maxDistance;
const bool inclusiveMax;
};
} // namespace mongo
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