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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/pipeline/document_source.h"
#include "mongo/db/pipeline/sequential_document_cache.h"
namespace mongo {
/**
* A DocumentSourceSequentialDocumentCache manages an underlying SequentialDocumentCache. If the
* cache's status is 'kBuilding', DocumentSourceSequentialDocumentCache will retrieve documents from
* the preceding pipeline stage, add them to the cache, and pass them through to the following
* pipeline stage. If the cache is in 'kServing' mode, DocumentSourceSequentialDocumentCache will
* return results directly from the cache rather than from a preceding stage. It does not have a
* registered parser and cannot be created from BSON.
*/
class DocumentSourceSequentialDocumentCache final : public DocumentSource {
public:
static constexpr StringData kStageName = "$sequentialCache"_sd;
const char* getSourceName() const final {
return DocumentSourceSequentialDocumentCache::kStageName.rawData();
}
StageConstraints constraints(Pipeline::SplitState pipeState) const {
StageConstraints constraints(StreamType::kStreaming,
_cache->isServing() ? PositionRequirement::kFirst
: PositionRequirement::kNone,
HostTypeRequirement::kNone,
DiskUseRequirement::kNoDiskUse,
FacetRequirement::kNotAllowed,
TransactionRequirement::kAllowed,
LookupRequirement::kAllowed,
UnionRequirement::kAllowed);
constraints.requiresInputDocSource = (_cache->isBuilding());
return constraints;
}
boost::optional<DistributedPlanLogic> distributedPlanLogic() final {
return boost::none;
}
static boost::intrusive_ptr<DocumentSourceSequentialDocumentCache> create(
const boost::intrusive_ptr<ExpressionContext>& pExpCtx, SequentialDocumentCache* cache) {
return new DocumentSourceSequentialDocumentCache(pExpCtx, cache);
}
/**
* Transitions the SequentialDocumentCache object's state to CacheStatus::kAbandoned. Once
* abandoned it is expected that the cache will not be used for subsequent operations.
*/
void abandonCache() {
invariant(_cache);
_cache->abandon();
}
/**
* The newly created DocumentSource will share a backing cache with the original DocumentSource
* that is being cloned. It is expected that only one of the DocumentSourceSequentialCache
* copies will be used, and therefore only one will actively be using the cache.
*/
boost::intrusive_ptr<DocumentSource> clone(
const boost::intrusive_ptr<ExpressionContext>& newExpCtx) const final {
auto newStage = create(newExpCtx ? newExpCtx : pExpCtx, _cache);
// Keep the position flag so in case the containing pipeline is cloned post-optimization.
newStage->_hasOptimizedPos = _hasOptimizedPos;
newStage->_cacheIsEOF = _cacheIsEOF;
return newStage;
}
protected:
GetNextResult doGetNext() final;
Pipeline::SourceContainer::iterator doOptimizeAt(Pipeline::SourceContainer::iterator itr,
Pipeline::SourceContainer* container) final;
private:
DocumentSourceSequentialDocumentCache(const boost::intrusive_ptr<ExpressionContext>& expCtx,
SequentialDocumentCache* cache);
Value serialize(boost::optional<ExplainOptions::Verbosity> explain = boost::none) const final;
SequentialDocumentCache* _cache;
// This flag is set to prevent the cache stage from immediately serving from the cache after it
// has exhausted input from its source for the first time.
bool _cacheIsEOF = false;
bool _hasOptimizedPos = false;
};
} // namespace mongo
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