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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 <deque>
#include "mongo/db/commands/server_status.h"
#include "mongo/db/operation_context.h"
#include "mongo/db/repl/member_data.h"
#include "mongo/db/repl/replication_coordinator_fwd.h"
#include "mongo/db/service_context.h"
#include "mongo/platform/atomic_word.h"
#include "mongo/stdx/mutex.h"
namespace mongo {
/**
* This class encapsulates (most) logic relating to throttling incoming writes when a primary
* discovers the commit point is lagging behind. The only method exposed to the system for
* functionality is the `sample` method. On a primary, replication will call that method every time
* new optimes are generated. FlowControl uses that to keep a data structure that can approximately
* answer the question: "How many operations are between two timestamps?"
*
* Otherwise this class' only output is to refresh the tickets available in the
* `FlowControlTicketholder`.
*/
class FlowControl : public ServerStatusSection {
public:
FlowControl(ServiceContext* service, repl::ReplicationCoordinator* replCoord);
/**
* Construct a flow control object without adding a periodic job runner for testing.
*/
FlowControl(repl::ReplicationCoordinator* replCoord);
static FlowControl* get(ServiceContext* service);
static FlowControl* get(ServiceContext& service);
static FlowControl* get(OperationContext* ctx);
static void set(ServiceContext* service, std::unique_ptr<FlowControl> flowControl);
int getNumTickets();
/**
* This method is called when replication is reserving `opsApplied` timestamps. `timestamp` is
* the timestamp in the oplog associated with the first oplog time being reserved.
*/
void sample(Timestamp timestamp, std::uint64_t opsApplied);
/**
* <ServerStatusSection>
*/
bool includeByDefault() const override {
return true;
}
/**
* <ServerStatusSection>
*/
BSONObj generateSection(OperationContext* opCtx,
const BSONElement& configElement) const override;
/**
* Underscore methods are public for testing.
*/
std::int64_t _getLocksUsedLastPeriod();
double _getLocksPerOp();
std::int64_t _approximateOpsBetween(Timestamp prevTs, Timestamp currTs);
void _updateTopologyData();
int _calculateNewTicketsForLag(const std::vector<repl::MemberData>& prevMemberData,
const std::vector<repl::MemberData>& currMemberData,
std::int64_t locksUsedLastPeriod,
double locksPerOp,
std::uint64_t lagMillis,
std::uint64_t thresholdLagMillis);
void _trimSamples(const Timestamp trimSamplesTo);
// Sample of (timestamp, ops, lock acquisitions) where ops and lock acquisitions are
// observations of the corresponding counter at (roughly) <timestamp>.
typedef std::tuple<std::uint64_t, std::uint64_t, std::int64_t> Sample;
const std::deque<Sample>& _getSampledOpsApplied_forTest() {
return _sampledOpsApplied;
}
private:
const int _kMaxTickets = 1000 * 1000 * 1000;
repl::ReplicationCoordinator* _replCoord;
// These values are updated with each flow control computation and are also surfaced in server
// status.
AtomicWord<int> _lastTargetTicketsPermitted{_kMaxTickets};
AtomicWord<double> _lastLocksPerOp{0.0};
AtomicWord<int> _lastSustainerAppliedCount{0};
AtomicWord<bool> _isLagged{false};
AtomicWord<int> _isLaggedCount{0};
// Use an int64_t as this is serialized to bson which does not support unsigned 64-bit numbers.
AtomicWord<std::int64_t> _isLaggedTimeMicros{0};
mutable stdx::mutex _sampledOpsMutex;
std::deque<Sample> _sampledOpsApplied;
// These values are used in the sampling process.
std::uint64_t _numOpsSinceStartup = 0;
std::uint64_t _lastSample = 0;
std::int64_t _lastPollLockAcquisitions = 0;
std::vector<repl::MemberData> _currMemberData;
std::vector<repl::MemberData> _prevMemberData;
Date_t _lastTimeSustainerAdvanced;
// This value is used for calculating server status metrics.
std::uint64_t _startWaitTime = 0;
PeriodicJobAnchor _jobAnchor;
};
} // namespace mongo
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