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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 "boost/optional.hpp"
#include <vector>
#include "mongo/base/disallow_copying.h"
#include "mongo/db/jsobj.h"
#include "mongo/db/record_id.h"
#include "mongo/db/storage/snapshot.h"
#include "mongo/stdx/unordered_set.h"
namespace mongo {
class IndexAccessMethod;
class WorkingSetMember;
typedef size_t WorkingSetID;
/**
* All data in use by a query. Data is passed through the stage tree by referencing the ID of
* an element of the working set. Stages can add elements to the working set, delete elements
* from the working set, or mutate elements in the working set.
*/
class WorkingSet {
MONGO_DISALLOW_COPYING(WorkingSet);
public:
static const WorkingSetID INVALID_ID = WorkingSetID(-1);
WorkingSet();
~WorkingSet();
/**
* Allocate a new query result and return the ID used to get and free it.
*/
WorkingSetID allocate();
/**
* Get the i-th mutable query result. The pointer will be valid for this id until freed.
* Do not delete the returned pointer as the WorkingSet retains ownership. Call free() to
* release it.
*/
WorkingSetMember* get(WorkingSetID i) const {
dassert(i < _data.size()); // ID has been allocated.
dassert(_data[i].nextFreeOrSelf == i); // ID currently in use.
return _data[i].member;
}
/**
* Returns true if WorkingSetMember with id 'i' is free.
*/
bool isFree(WorkingSetID i) const {
return _data[i].nextFreeOrSelf != i;
}
/**
* Deallocate the i-th query result and release its resources.
*/
void free(WorkingSetID i);
/**
* Removes and deallocates all members of this working set.
*/
void clear();
//
// WorkingSetMember state transitions
//
void transitionToRecordIdAndIdx(WorkingSetID id);
void transitionToRecordIdAndObj(WorkingSetID id);
void transitionToOwnedObj(WorkingSetID id);
/**
* Returns the list of working set ids that have transitioned into the RID_AND_IDX state since
* the last yield. The members corresponding to these ids may have since transitioned to a
* different state or been freed, so these cases must be handled by the caller. The list may
* also contain duplicates.
*
* Execution stages are *not* responsible for managing this list, as working set ids are added
* to the set automatically by WorkingSet::transitionToRecordIdAndIdx().
*
* As a side effect, calling this method clears the list of flagged yield sensitive ids kept by
* the working set.
*/
std::vector<WorkingSetID> getAndClearYieldSensitiveIds();
private:
struct MemberHolder {
MemberHolder();
~MemberHolder();
// Free list link if freed. Points to self if in use.
WorkingSetID nextFreeOrSelf;
// Owning pointer
WorkingSetMember* member;
};
// All WorkingSetIDs are indexes into this, except for INVALID_ID.
// Elements are added to _freeList rather than removed when freed.
std::vector<MemberHolder> _data;
// Index into _data, forming a linked-list using MemberHolder::nextFreeOrSelf as the next
// link. INVALID_ID is the list terminator since 0 is a valid index.
// If _freeList == INVALID_ID, the free list is empty and all elements in _data are in use.
WorkingSetID _freeList;
// Contains ids of WSMs that may need to be adjusted when we next yield.
std::vector<WorkingSetID> _yieldSensitiveIds;
};
/**
* The key data extracted from an index. Keeps track of both the key (currently a BSONObj) and
* the index that provided the key. The index key pattern is required to correctly interpret
* the key.
*/
struct IndexKeyDatum {
IndexKeyDatum(const BSONObj& keyPattern, const BSONObj& key, const IndexAccessMethod* index)
: indexKeyPattern(keyPattern), keyData(key), index(index) {}
/**
* getFieldDotted produces the field with the provided name based on index keyData. The return
* object is populated if the element is in a provided index key. Returns none otherwise.
* Returning none indicates a query planning error.
*/
static boost::optional<BSONElement> getFieldDotted(const std::vector<IndexKeyDatum>& keyData,
const std::string& field) {
for (size_t i = 0; i < keyData.size(); ++i) {
BSONObjIterator keyPatternIt(keyData[i].indexKeyPattern);
BSONObjIterator keyDataIt(keyData[i].keyData);
while (keyPatternIt.more()) {
BSONElement keyPatternElt = keyPatternIt.next();
verify(keyDataIt.more());
BSONElement keyDataElt = keyDataIt.next();
if (field == keyPatternElt.fieldName())
return boost::make_optional(keyDataElt);
}
}
return boost::none;
}
// This is not owned and points into the IndexDescriptor's data.
BSONObj indexKeyPattern;
// This is the BSONObj for the key that we put into the index. Owned by us.
BSONObj keyData;
const IndexAccessMethod* index;
};
/**
* What types of computed data can we have?
*/
enum WorkingSetComputedDataType {
// What's the score of the document retrieved from a $text query?
WSM_COMPUTED_TEXT_SCORE = 0,
// What's the distance from a geoNear query point to the document?
WSM_COMPUTED_GEO_DISTANCE = 1,
// The index key used to retrieve the document, for returnKey query option.
WSM_INDEX_KEY = 2,
// What point (of several possible points) was used to compute the distance to the document
// via geoNear?
WSM_GEO_NEAR_POINT = 3,
// Comparison key for sorting.
WSM_SORT_KEY = 4,
// Must be last.
WSM_COMPUTED_NUM_TYPES,
};
/**
* Data that is a computed function of a WSM.
*/
class WorkingSetComputedData {
MONGO_DISALLOW_COPYING(WorkingSetComputedData);
public:
WorkingSetComputedData(const WorkingSetComputedDataType type) : _type(type) {}
virtual ~WorkingSetComputedData() {}
WorkingSetComputedDataType type() const {
return _type;
}
virtual WorkingSetComputedData* clone() const = 0;
private:
WorkingSetComputedDataType _type;
};
/**
* The type of the data passed between query stages. In particular:
*
* Index scan stages return a WorkingSetMember in the RID_AND_IDX state.
*
* Collection scan stages return a WorkingSetMember in the RID_AND_OBJ state.
*
* A WorkingSetMember may have any of the data above.
*/
class WorkingSetMember {
MONGO_DISALLOW_COPYING(WorkingSetMember);
public:
WorkingSetMember();
~WorkingSetMember();
/**
* Reset to an "empty" state.
*/
void clear();
enum MemberState {
// Initial state.
INVALID,
// Data is from 1 or more indices.
RID_AND_IDX,
// Data is from a collection scan, or data is from an index scan and was fetched. The
// BSONObj might be owned or unowned.
RID_AND_OBJ,
// The WSM doesn't correspond to an on-disk document anymore (e.g. is a computed
// expression). Since it doesn't correspond to a stored document, a WSM in this state has an
// owned BSONObj, but no record id.
OWNED_OBJ,
};
//
// Member state and state transitions
//
MemberState getState() const;
void transitionToOwnedObj();
//
// Core attributes
//
RecordId recordId;
Snapshotted<BSONObj> obj;
std::vector<IndexKeyDatum> keyData;
// True if this WSM has survived a yield in RID_AND_IDX state.
// TODO consider replacing by tracking SnapshotIds for IndexKeyDatums.
bool isSuspicious = false;
bool hasRecordId() const;
bool hasObj() const;
bool hasOwnedObj() const;
/**
* Ensures that 'obj' of a WSM in the RID_AND_OBJ state is owned BSON. It is a no-op if the WSM
* is in a different state or if 'obj' is already owned.
*
* It is illegal for unowned BSON to survive a yield, so this must be called on any working set
* members which may stay alive across yield points.
*/
void makeObjOwnedIfNeeded();
//
// Computed data
//
bool hasComputed(const WorkingSetComputedDataType type) const;
const WorkingSetComputedData* getComputed(const WorkingSetComputedDataType type) const;
void addComputed(WorkingSetComputedData* data);
/**
* getFieldDotted uses its state (obj or index data) to produce the field with the provided
* name.
*
* Returns true if there is the element is in an index key or in an (owned or unowned)
* object. *out is set to the element if so.
*
* Returns false otherwise. Returning false indicates a query planning error.
*/
bool getFieldDotted(const std::string& field, BSONElement* out) const;
/**
* Returns expected memory usage of working set member.
*/
size_t getMemUsage() const;
private:
friend class WorkingSet;
MemberState _state = WorkingSetMember::INVALID;
std::unique_ptr<WorkingSetComputedData> _computed[WSM_COMPUTED_NUM_TYPES];
};
} // namespace mongo
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