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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 "mongo/db/exec/requires_index_stage.h"
#include "mongo/db/index/index_access_method.h"
#include "mongo/db/matcher/expression.h"
#include "mongo/db/query/index_bounds.h"
#include "mongo/db/record_id.h"
namespace mongo {
class IndexAccessMethod;
class IndexDescriptor;
class WorkingSet;
struct DistinctParams {
DistinctParams(const IndexDescriptor* descriptor,
std::string indexName,
BSONObj keyPattern,
MultikeyPaths multikeyPaths,
bool multikey)
: indexDescriptor(descriptor),
name(std::move(indexName)),
keyPattern(std::move(keyPattern)),
multikeyPaths(std::move(multikeyPaths)),
isMultiKey(multikey) {
invariant(indexDescriptor);
}
DistinctParams(OperationContext* opCtx, const IndexDescriptor* descriptor)
: DistinctParams(descriptor,
descriptor->indexName(),
descriptor->keyPattern(),
descriptor->getEntry()->getMultikeyPaths(opCtx),
descriptor->getEntry()->isMultikey()) {}
const IndexDescriptor* indexDescriptor;
std::string name;
BSONObj keyPattern;
MultikeyPaths multikeyPaths;
bool isMultiKey;
int scanDirection{1};
// 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{0};
};
/**
* 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 final : public RequiresIndexStage {
public:
DistinctScan(ExpressionContext* expCtx,
const CollectionPtr& collection,
DistinctParams params,
WorkingSet* workingSet);
StageState doWork(WorkingSetID* out) final;
bool isEOF() final;
void doDetachFromOperationContext() final;
void doReattachToOperationContext() final;
StageType stageType() const final {
return STAGE_DISTINCT_SCAN;
}
std::unique_ptr<PlanStageStats> getStats() final;
const SpecificStats* getSpecificStats() const final;
static const char* kStageType;
protected:
void doSaveStateRequiresIndex() final;
void doRestoreStateRequiresIndex() final;
private:
// The WorkingSet we annotate with results. Not owned by us.
WorkingSet* _workingSet;
const BSONObj _keyPattern;
const int _scanDirection = 1;
const IndexBounds _bounds;
const int _fieldNo = 0;
// The cursor we use to navigate the tree.
std::unique_ptr<SortedDataInterface::Cursor> _cursor;
// _checker gives us our start key and ensures we stay in bounds.
IndexBoundsChecker _checker;
IndexSeekPoint _seekPoint;
// Stats
DistinctScanStats _specificStats;
};
} // namespace mongo
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