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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/plan_stage.h"
#include "mongo/db/query/count_request.h"
namespace mongo {
struct CountStageParams {
CountStageParams(const CountRequest& request, bool useRecordStoreCount)
: nss(request.getNs()),
limit(request.getLimit()),
skip(request.getSkip()),
useRecordStoreCount(useRecordStoreCount) {}
// Namespace to operate on (e.g. "foo.bar").
NamespaceString nss;
// An integer limiting the number of documents to count. 0 means no limit.
long long limit;
// An integer indicating to not include the first n documents in the count. 0 means no skip.
long long skip;
// True if this count stage should just ask the record store for a count instead of computing
// one itself.
//
// Note: This strategy can lead to inaccurate counts on certain storage engines (including
// WiredTiger).
bool useRecordStoreCount;
};
/**
* Stage used by the count command. This stage sits at the root of a plan tree
* and counts the number of results returned by its child stage.
*
* This should not be confused with the CountScan stage. CountScan is a special
* index access stage which can optimize index access for count operations in
* some cases. On the other hand, *every* count op has a CountStage at its root.
*
* Only returns NEED_TIME until hitting EOF. The count result can be obtained by examining
* the specific stats.
*/
class CountStage final : public PlanStage {
public:
CountStage(OperationContext* opCtx,
Collection* collection,
CountStageParams params,
WorkingSet* ws,
PlanStage* child);
bool isEOF() final;
StageState doWork(WorkingSetID* out) final;
StageType stageType() const final {
return STAGE_COUNT;
}
std::unique_ptr<PlanStageStats> getStats();
const SpecificStats* getSpecificStats() const final;
static const char* kStageType;
private:
/**
* Asks the record store for the count, applying the skip and limit if necessary. The result is
* stored in '_specificStats'.
*
* This is only valid if the query and hint are both empty.
*/
void recordStoreCount();
// The collection over which we are counting.
Collection* _collection;
CountStageParams _params;
// The number of documents that we still need to skip.
long long _leftToSkip;
// The working set used to pass intermediate results between stages. Not owned
// by us.
WorkingSet* _ws;
CountStats _specificStats;
};
} // namespace mongo
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