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/**
* Copyright (C) 2016 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 "mongo/db/pipeline/document_source.h"
#include "mongo/db/pipeline/document_source_sort.h"
namespace mongo {
class DocumentSourceSample final : public DocumentSource, public NeedsMergerDocumentSource {
public:
static constexpr StringData kStageName = "$sample"_sd;
GetNextResult getNext() final;
const char* getSourceName() const final {
return kStageName.rawData();
}
Value serialize(boost::optional<ExplainOptions::Verbosity> explain = boost::none) const final;
StageConstraints constraints(Pipeline::SplitState pipeState) const final {
return {StreamType::kBlocking,
PositionRequirement::kNone,
HostTypeRequirement::kNone,
DiskUseRequirement::kWritesTmpData,
FacetRequirement::kAllowed,
TransactionRequirement::kAllowed};
}
DepsTracker::State getDependencies(DepsTracker* deps) const final {
return DepsTracker::State::SEE_NEXT;
}
boost::intrusive_ptr<DocumentSource> getShardSource() final;
MergingLogic mergingLogic() final;
long long getSampleSize() const {
return _size;
}
static boost::intrusive_ptr<DocumentSource> createFromBson(
BSONElement elem, const boost::intrusive_ptr<ExpressionContext>& expCtx);
private:
explicit DocumentSourceSample(const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
long long _size;
// Uses a $sort stage to randomly sort the documents.
boost::intrusive_ptr<DocumentSourceSort> _sortStage;
};
} // namespace mongo
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