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/**
* Copyright (C) 2022-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/concurrency/lock_manager_defs.h"
#include "mongo/util/tick_source.h"
#include <boost/optional.hpp>
namespace mongo {
/**
* Stores state and statistics related to admission control for a given transactional context.
*/
class AdmissionContext {
public:
AdmissionContext() {}
/**
* Classifies the priority that an operation acquires a ticket when the system is under high
* load (operations are throttled waiting for a ticket). Only applicable when there are no
* available tickets.
*
* 'kLow': It's of low importance that the operation acquires a ticket. These low-priority
* operations are reserved for background tasks that have no other operations dependent on them.
* These operations may be throttled under load and make significantly less progress as compared
* to operations of a higher priority.
*
* 'kNormal': It's important that the operation be throttled under load. If this operation is
* throttled, it will not affect system availability or observability. Most operations, both
* user and internal, should use this priority unless they qualify as 'kLow' or 'kHigh'
* priority.
*
* 'kHigh': It's crucial that the operation makes forward progress - bypassing ticket
* acquisition. Reserved for operations critical to availability (e.g. replication workers) or
* observability (e.g. FTDC), and any operation that is releasing resources (e.g. committing or
* aborting prepared transactions). Should be used sparingly.
*
* TODO SERVER-67951: Update comment to address that kHigh priority operations are always
* granted a ticket immediately upon request.
*/
enum class AcquisitionPriority { kLow, kNormal, kHigh };
void start(TickSource* tickSource) {
admissions++;
if (tickSource) {
_startProcessingTime = tickSource->getTicks();
}
}
TickSource::Tick getStartProcessingTime() const {
return _startProcessingTime;
}
/**
* Returns the number of times this context has taken a ticket.
*/
int getAdmissions() const {
return admissions;
}
void setLockMode(LockMode lockMode) {
_lockMode = lockMode;
}
LockMode getLockMode() const {
return _lockMode;
}
void setPriority(AcquisitionPriority priority) {
_priority = priority;
}
AcquisitionPriority getPriority() const {
invariant(_priority);
return _priority.get();
}
private:
TickSource::Tick _startProcessingTime{0};
int admissions{0};
LockMode _lockMode = LockMode::MODE_NONE;
// TODO SERVER-68933: Don't default _priority to kNormal.
boost::optional<AcquisitionPriority> _priority{AcquisitionPriority::kNormal};
};
} // namespace mongo
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