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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 <vector>
#include "mongo/db/s/transaction_coordinator_util.h"
#include "mongo/util/fail_point.h"
namespace mongo {
class TransactionCoordinatorMetricsObserver;
/**
* State machine, which implements the two-phase commit protocol for a specific transaction,
* identified by lsid + txnNumber + txnRetryCounter.
*
* The lifetime of a coordinator starts with a construction and ends with the `onCompletion()`
* future getting signaled. It is illegal to destroy a coordinator without waiting for
* `onCompletion()`.
*/
class TransactionCoordinator {
TransactionCoordinator(const TransactionCoordinator&) = delete;
TransactionCoordinator& operator=(const TransactionCoordinator&) = delete;
public:
/**
* The two-phase commit steps.
*/
enum class Step {
kInactive,
kWritingParticipantList,
kWaitingForVotes,
kWritingDecision,
kWaitingForDecisionAcks,
kDeletingCoordinatorDoc,
};
/**
* Instantiates a new TransactionCoordinator for the specified lsid + txnNumber +
* txnRetryCounter and gives it a 'scheduler' to use for any asynchronous tasks it spawns.
*
* If the 'coordinateCommitDeadline' parameter is specified, a timed task will be scheduled to
* cause the coordinator to be put in a cancelled state, if runCommit is not eventually
* received.
*/
TransactionCoordinator(OperationContext* operationContext,
const LogicalSessionId& lsid,
const TxnNumberAndRetryCounter& txnNumberAndRetryCounter,
std::unique_ptr<txn::AsyncWorkScheduler> scheduler,
Date_t deadline);
~TransactionCoordinator();
/**
* The first time this is called, it asynchronously begins the two-phase commit process for the
* transaction that this coordinator is responsible for.
*
* Subsequent calls will not re-run the commit process.
*/
void runCommit(OperationContext* opCtx, std::vector<ShardId> participantShards);
/**
* To be used to continue coordinating a transaction on step up.
*/
void continueCommit(const txn::TransactionCoordinatorDocument& doc);
/**
* Gets a Future that will contain the decision that the coordinator reaches. Note that this
* will never be signaled unless runCommit has been called.
*/
SharedSemiFuture<txn::CommitDecision> getDecision() const;
/**
* Returns a future which can be listened on for when all the asynchronous activity spawned by
* this coordinator has completed. It will always eventually be set and once set it is safe to
* dispose of the TransactionCoordinator object.
*/
SharedSemiFuture<txn::CommitDecision> onCompletion();
/**
* If runCommit has not yet been called, this will transition this coordinator object to
* the 'done' state, effectively making it impossible for two-phase commit to be run for this
* coordinator.
*
* Called when a transaction with a higher transaction number is received on this session or
* when the transaction coordinator service is shutting down.
*/
void cancelIfCommitNotYetStarted();
TxnRetryCounter getTxnRetryCounterForTest() const {
return *_txnNumberAndRetryCounter.getTxnRetryCounter();
}
/**
* Returns the TransactionCoordinatorMetricsObserver for this TransactionCoordinator.
*/
const TransactionCoordinatorMetricsObserver& getMetricsObserverForTest() {
return *_transactionCoordinatorMetricsObserver;
}
void reportState(BSONObjBuilder& parent) const;
std::string toString(Step step) const;
Step getStep() const;
private:
void _updateAssociatedClient(Client* client);
bool _reserveKickOffCommitPromise();
/**
* Helper for handling errors that occur during either phase of commit coordination.
*/
void _done(Status s);
/**
* Logs the diagnostic string for a commit coordination.
*/
void _logSlowTwoPhaseCommit(const txn::CoordinatorCommitDecision& decision);
/**
* Builds the diagnostic string for a commit coordination.
*/
std::string _twoPhaseCommitInfoForLog(const txn::CoordinatorCommitDecision& decision) const;
// Shortcut to the service context under which this coordinator runs
ServiceContext* const _serviceContext;
// The lsid + txnNumber + txnRetryCounter that this coordinator is coordinating.
const LogicalSessionId _lsid;
const TxnNumberAndRetryCounter _txnNumberAndRetryCounter;
// Scheduler and context wrapping all asynchronous work dispatched by this coordinator
std::unique_ptr<txn::AsyncWorkScheduler> _scheduler;
// Scheduler used for the persist participants + prepare part of the 2PC sequence and
// interrupted separately from the rest of the chain in order to allow the clean-up tasks
// (running on _scheduler to still be able to execute).
std::unique_ptr<txn::AsyncWorkScheduler> _sendPrepareScheduler;
// Protects the state below
mutable Mutex _mutex = MONGO_MAKE_LATCH("TransactionCoordinator::_mutex");
// Tracks which step of the 2PC coordination is currently (or was most recently) executing
Step _step{Step::kInactive};
// Promise/future pair which will be signaled when the coordinator has completed
bool _kickOffCommitPromiseSet{false};
Promise<void> _kickOffCommitPromise;
// The state below gets populated sequentially as the coordinator advances through the 2 phase
// commit stages. Each of these fields is set only once for the lifetime of a coordinator and
// after that never changes.
//
// If the coordinator is canceled before commit is requested, none of these fiends will be set
// Set when the coordinator has been asked to coordinate commit
boost::optional<txn::ParticipantsList> _participants;
bool _participantsDurable{false};
// Set when the coordinator has heard back from all the participants and reached a decision, but
// hasn't yet persisted it
boost::optional<txn::CoordinatorCommitDecision> _decision;
// Set when the coordinator has durably persisted `_decision` to the `config.coordinators`
// collection
bool _decisionDurable{false};
SharedPromise<txn::CommitDecision> _decisionPromise;
// A list of all promises corresponding to futures that were returned to callers of
// onCompletion.
SharedPromise<txn::CommitDecision> _completionPromise;
// Store as unique_ptr to avoid a circular dependency between the TransactionCoordinator and
// the TransactionCoordinatorMetricsObserver.
std::unique_ptr<TransactionCoordinatorMetricsObserver> _transactionCoordinatorMetricsObserver;
// The deadline for the TransactionCoordinator to reach a decision
Date_t _deadline;
};
} // namespace mongo
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