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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/logical_session_id.h"
#include "mongo/db/s/transaction_coordinator_futures_util.h"
#include "mongo/executor/task_executor.h"
#include "mongo/util/concurrency/thread_pool.h"
#include "mongo/util/future.h"
namespace mongo {
class TransactionCoordinatorDocument;
namespace txn {
/**
* The decision made by the coordinator whether to commit or abort the transaction.
*/
enum class CommitDecision {
kCommit,
kAbort,
kCanceled,
};
/**
* An alias to indicate a vote from a participant. This just makes it clearer what's going on in
* different stages of the commit process.
*/
using PrepareVote = CommitDecision;
/**
* Represents a response to prepareTransaction from a single participant. The timestamp will only be
* present if the participant votes to commit (indicated by the decision field).
*/
struct PrepareResponse {
ShardId participantShardId;
boost::optional<PrepareVote> vote;
boost::optional<Timestamp> prepareTimestamp;
};
/**
* Represents the aggregate of all prepare responses, including the decision that should be made and
* the max of all prepare timestamps received in the case of a decision to commit.
*/
struct PrepareVoteConsensus {
boost::optional<CommitDecision> decision;
boost::optional<Timestamp> maxPrepareTimestamp;
};
} // namespace txn
/**
* Single instance of this class is owned by each TransactionCoordinator. It abstracts the
* long-running blocking operations into a futurized interface and ensures that all outstanding
* operations are joined at completion.
*
* Methods on this class must be called from a single thread at a time and other than cancellation,
* no other operations are allowed until any returned futures are signalled.
*/
class TransactionCoordinatorDriver {
MONGO_DISALLOW_COPYING(TransactionCoordinatorDriver);
public:
TransactionCoordinatorDriver(ServiceContext* serviceContext);
~TransactionCoordinatorDriver();
/**
* Upserts a document of the form:
*
* {
* _id: {lsid: <lsid>, txnNumber: <txnNumber>}
* participants: ["shard0000", "shard0001"]
* }
*
* into config.transaction_coordinators and waits for the upsert to be majority-committed.
*
* Throws if the upsert fails or waiting for writeConcern fails.
*
* If the upsert returns a DuplicateKey error, converts it to an anonymous error, because it
* means a document for the (lsid, txnNumber) exists with a different participant list.
*/
Future<void> persistParticipantList(const LogicalSessionId& lsid,
TxnNumber txnNumber,
std::vector<ShardId> participantList);
/**
* Sends prepare to all participants and returns a future that will be resolved when either:
* a) All participants have responded with a vote to commit, or
* b) At least one participant votes to abort.
*
* If all participants vote to commit, the result will contain the max prepare timestamp of all
* prepare timestamps attached to the participants' responses. Otherwise the result will simply
* contain the decision to abort.
*/
Future<txn::PrepareVoteConsensus> sendPrepare(const std::vector<ShardId>& participantShards,
const LogicalSessionId& lsid,
TxnNumber txnNumber);
/**
* If 'commitTimestamp' is boost::none, updates the document in config.transaction_coordinators
* for
*
* (lsid, txnNumber) to be:
*
* {
* _id: {lsid: <lsid>, txnNumber: <txnNumber>}
* participants: ["shard0000", "shard0001"]
* decision: "abort"
* }
*
* else updates the document to be:
*
* {
* _id: {lsid: <lsid>, txnNumber: <txnNumber>}
* participants: ["shard0000", "shard0001"]
* decision: "commit"
* commitTimestamp: Timestamp(xxxxxxxx, x),
* }
*
* and waits for the update to be majority-committed.
*
* Throws if the update fails or waiting for writeConcern fails.
*
* If the update succeeds but did not update any document, throws an anonymous error, because it
* means either no document for (lsid, txnNumber) exists, or a document exists but has a
* different participant list, different decision, or different commit Timestamp.
*/
Future<void> persistDecision(const LogicalSessionId& lsid,
TxnNumber txnNumber,
std::vector<ShardId> participantList,
const boost::optional<Timestamp>& commitTimestamp);
/**
* Sends commit to all shards and returns a future that will be resolved when all participants
* have responded with success.
*/
Future<void> sendCommit(const std::vector<ShardId>& participantShards,
const LogicalSessionId& lsid,
TxnNumber txnNumber,
Timestamp commitTimestamp);
/**
* Sends abort to all shards and returns a future that will be resolved when all participants
* have responded with success.
*/
Future<void> sendAbort(const std::vector<ShardId>& participantShards,
const LogicalSessionId& lsid,
TxnNumber txnNumber);
/**
* Deletes the document in config.transaction_coordinators for (lsid, txnNumber).
*
* Does *not* wait for the delete to be majority-committed.
*
* Throws if the update fails.
*
* If the update succeeds but did not update any document, throws an anonymous error, because it
* means either no document for (lsid, txnNumber) exists, or a document exists but without a
* decision.
*/
Future<void> deleteCoordinatorDoc(const LogicalSessionId& lsid, TxnNumber txnNumber);
/**
* Non-blocking method, which interrupts any executing asynchronous tasks and prevents new ones
* from getting scheduled. Any futures returned by the driver must still be waited on before the
* object is disposed of.
*
* TODO (SERVER-38522): Implement using real cancellation through the AsyncWorkScheduler
*/
void cancel();
/**
* Reads and returns all documents in config.transaction_coordinators.
*/
static std::vector<TransactionCoordinatorDocument> readAllCoordinatorDocs(
OperationContext* opCtx);
//
// These methods are used internally and are exposed for unit-testing purposes only
//
/**
* Sends prepare to a given shard, retrying until a response is received from the participant or
* until the coordinator is no longer in a preparing state due to having already received a vote
* to abort from another participant.
*
* Returns a future containing the participant's response.
*/
Future<txn::PrepareResponse> sendPrepareToShard(const ShardId& shardId,
const BSONObj& prepareCommandObj);
/**
* Sends a command corresponding to a commit decision (i.e. commitTransaction or
* abortTransaction) to the given shard ID and retries on any retryable error until the command
* succeeds or receives a response that may be interpreted as a vote to abort (e.g.
* NoSuchTransaction).
*
* Used for sendCommit and sendAbort.
*/
Future<void> sendDecisionToParticipantShard(const ShardId& shardId, const BSONObj& commandObj);
private:
ServiceContext* _serviceContext;
std::unique_ptr<txn::AsyncWorkScheduler> _scheduler;
// TODO (SERVER-38522): Remove once AsyncWorkScheduler is used for cancellation
AtomicWord<bool> _cancelled{false};
};
} // namespace mongo
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