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/**
* Copyright (C) 2014 MongoDB Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* 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
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* 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 GNU Affero General 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/scoped_ptr.hpp>
#include "mongo/db/exec/plan_stage.h"
#include "mongo/db/index/btree_index_cursor.h"
#include "mongo/db/index/index_access_method.h"
#include "mongo/db/jsobj.h"
#include "mongo/db/matcher/expression.h"
#include "mongo/db/query/index_bounds.h"
#include "mongo/db/record_id.h"
#include "mongo/platform/unordered_set.h"
namespace mongo {
class IndexAccessMethod;
class IndexCursor;
class IndexDescriptor;
class WorkingSet;
struct DistinctParams {
DistinctParams() : descriptor(NULL),
direction(1),
fieldNo(0) { }
// What index are we traversing?
const IndexDescriptor* descriptor;
// And in what direction?
int direction;
// What are the bounds?
IndexBounds bounds;
// What field in the index's key pattern is the one we're distinct-ing over?
// For example:
// If we have an index {a:1, b:1} we could use it to distinct over either 'a' or 'b'.
// If we distinct over 'a' the position is 0.
// If we distinct over 'b' the position is 1.
int fieldNo;
};
/**
* Used by the distinct command. Executes a mutated index scan over the provided bounds.
* However, rather than looking at every key in the bounds, it skips to the next value of the
* _params.fieldNo-th indexed field. This is because distinct only cares about distinct values
* for that field, so there is no point in examining all keys with the same value for that
* field.
*
* Only created through the getExecutorDistinct path. See db/query/get_executor.cpp
*/
class DistinctScan : public PlanStage {
public:
/**
* Keeps track of what this distinct scan is currently doing so that it
* can do the right thing on the next call to work().
*/
enum ScanState {
// Need to initialize the underlying index traversal machinery.
INITIALIZING,
// Skipping keys in order to check whether we have reached the end.
CHECKING_END,
// Retrieving the next key, and applying the filter if necessary.
GETTING_NEXT,
// The index scan is finished.
HIT_END
};
DistinctScan(OperationContext* txn, const DistinctParams& params, WorkingSet* workingSet);
virtual ~DistinctScan() { }
virtual StageState work(WorkingSetID* out);
virtual bool isEOF();
virtual void saveState();
virtual void restoreState(OperationContext* opCtx);
virtual void invalidate(OperationContext* txn, const RecordId& dl, InvalidationType type);
virtual std::vector<PlanStage*> getChildren() const;
virtual StageType stageType() const { return STAGE_DISTINCT; }
virtual PlanStageStats* getStats();
virtual const CommonStats* getCommonStats();
virtual const SpecificStats* getSpecificStats();
static const char* kStageType;
private:
/**
* Initialize the underlying IndexCursor
*/
void initIndexCursor();
/** See if the cursor is pointing at or past _endKey, if _endKey is non-empty. */
void checkEnd();
// transactional context for read locks. Not owned by us
OperationContext* _txn;
// The WorkingSet we annotate with results. Not owned by us.
WorkingSet* _workingSet;
// Index access.
const IndexDescriptor* _descriptor; // owned by Collection -> IndexCatalog
const IndexAccessMethod* _iam; // owned by Collection -> IndexCatalog
// The cursor we use to navigate the tree.
boost::scoped_ptr<BtreeIndexCursor> _btreeCursor;
// Keeps track of what work we need to do next.
ScanState _scanState;
// For yielding.
BSONObj _savedKey;
RecordId _savedLoc;
DistinctParams _params;
// _checker gives us our start key and ensures we stay in bounds.
boost::scoped_ptr<IndexBoundsChecker> _checker;
int _keyEltsToUse;
bool _movePastKeyElts;
std::vector<const BSONElement*> _keyElts;
std::vector<bool> _keyEltsInc;
// Stats
CommonStats _commonStats;
DistinctScanStats _specificStats;
};
} // namespace mongo
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