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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 <boost/optional.hpp>
#include <map>
#include "mongo/base/disallow_copying.h"
#include "mongo/db/commands/txn_cmds_gen.h"
#include "mongo/db/logical_session_id.h"
#include "mongo/db/operation_context.h"
#include "mongo/db/repl/read_concern_args.h"
#include "mongo/s/async_requests_sender.h"
#include "mongo/s/client/shard.h"
#include "mongo/s/shard_id.h"
#include "mongo/util/string_map.h"
namespace mongo {
/**
* Keeps track of the transaction state. A session is in use when it is being used by a request.
*/
class TransactionRouter {
public:
// The default value to use as the statement id of the first command in the transaction if none
// was sent.
static const StmtId kDefaultFirstStmtId = 0;
/**
* Represents the options for a transaction that are shared across all participants. These
* cannot be changed without restarting the transactions that may have already been begun on
* every participant, i.e. clearing the current participant list.
*/
struct SharedTransactionOptions {
// Set for all distributed transactions.
TxnNumber txnNumber;
repl::ReadConcernArgs readConcernArgs;
// Only set for transactions with snapshot level read concern.
boost::optional<LogicalTime> atClusterTime;
};
/**
* Represents a shard participant in a distributed transaction. Lives only for the duration of
* the transaction that created it.
*/
struct Participant {
Participant(bool isCoordinator,
StmtId stmtIdCreatedAt,
SharedTransactionOptions sharedOptions);
/**
* Attaches necessary fields if this is participating in a multi statement transaction.
*/
BSONObj attachTxnFieldsIfNeeded(BSONObj cmd, bool isFirstStatementInThisParticipant) const;
// True if the participant has been chosen as the coordinator for its transaction
const bool isCoordinator{false};
// The highest statement id of the request during which this participant was created.
const StmtId stmtIdCreatedAt{kUninitializedStmtId};
// Returns the shared transaction options this participant was created with
const SharedTransactionOptions sharedOptions;
};
enum class TransactionActions { kStart, kContinue, kCommit };
/**
* Encapsulates the logic around selecting a global read timestamp for a sharded transaction at
* snapshot level read concern.
*
* The first command in a transaction to target at least one shard must select a cluster time
* timestamp before targeting, but may change the timestamp before contacting any shards to
* allow optimizing the timestamp based on the targeted shards. If the first command encounters
* a retryable error, e.g. StaleShardVersion or SnapshotTooOld, the retry may also select a new
* timestamp. Once the first command has successfully completed, the timestamp cannot be
* changed.
*/
class AtClusterTime {
public:
/**
* Cannot be called until a timestamp has been set.
*/
LogicalTime getTime() const;
/**
* Sets the timestamp and remembers the statement id of the command that set it.
*/
void setTime(LogicalTime atClusterTime, StmtId currentStmtId);
/**
* True if the timestamp can be changed by a command running at the given statement id.
*/
bool canChange(StmtId currentStmtId) const;
private:
StmtId _stmtIdSelectedAt = kUninitializedStmtId;
LogicalTime _atClusterTime;
};
TransactionRouter();
~TransactionRouter();
/**
* Extract the runtime state attached to the operation context. Returns nullptr if none is
* attached.
*/
static TransactionRouter* get(OperationContext* opCtx);
/**
* Starts a fresh transaction in this session or continue an existing one. Also cleans up the
* previous transaction state.
*/
void beginOrContinueTxn(OperationContext* opCtx,
TxnNumber txnNumber,
TransactionActions action);
/**
* Attaches the required transaction related fields for a request to be sent to the given
* shard.
*
* Calling this method has the following side effects:
* 1. Potentially selecting a coordinator.
* 2. Adding the shard to the list of participants.
* 3. Also append fields for first statements (ex. startTransaction, readConcern)
* if the shard was newly added to the list of participants.
*/
BSONObj attachTxnFieldsIfNeeded(const ShardId& shardId, const BSONObj& cmdObj);
/**
* Returns true if the current transaction can retry on a stale version error from a contacted
* shard. This is always true except for an error received by a write that is not the first
* overall statement in the sharded transaction. This is because the entire command will be
* retried, and shards that were not stale and are targeted again may incorrectly execute the
* command a second time.
*
* Note: Even if this method returns true, the retry attempt may still fail, e.g. if one of the
* shards that returned a stale version error was involved in a previously completed a statement
* for this transaction.
*
* TODO SERVER-37207: Change batch writes to retry only the failed writes in a batch, to allow
* retrying writes beyond the first overall statement.
*/
bool canContinueOnStaleShardOrDbError(StringData cmdName) const;
/**
* Updates the transaction state to allow for a retry of the current command on a stale version
* error. This includes sending abortTransaction to all cleared participants. Will throw if the
* transaction cannot be continued.
*/
void onStaleShardOrDbError(OperationContext* opCtx,
StringData cmdName,
const Status& errorStatus);
/**
* Returns true if the current transaction can retry on a snapshot error. This is only true on
* the first command recevied for a transaction.
*/
bool canContinueOnSnapshotError() const;
/**
* Resets the transaction state to allow for a retry attempt. This includes clearing all
* participants, clearing the coordinator, resetting the global read timestamp, and sending
* abortTransaction to all cleared participants. Will throw if the transaction cannot be
* continued.
*/
void onSnapshotError(OperationContext* opCtx, const Status& errorStatus);
/**
* Updates the transaction tracking state to allow for a retry attempt on a view resolution
* error. This includes sending abortTransaction to all cleared participants.
*/
void onViewResolutionError(OperationContext* opCtx, const NamespaceString& nss);
/**
* Sets the atClusterTime for the current transaction to the latest time in the router's logical
* clock. Does nothing if the transaction does not have snapshot read concern or an
* atClusterTime has already been selected and cannot be changed.
*/
void setDefaultAtClusterTime(OperationContext* opCtx);
/**
* Returns the global read timestamp for this transaction. Returns boost::none for transactions
* that don't run at snapshot level read concern or if a timestamp has not yet been selected.
*/
const boost::optional<AtClusterTime>& getAtClusterTime() const;
/**
* If a coordinator has been selected for the current transaction, returns its identifier
*/
const boost::optional<ShardId>& getCoordinatorId() const;
/**
* Commits the transaction. For transactions with multiple participants, this will initiate
* the two phase commit procedure.
*/
Shard::CommandResponse commitTransaction(
OperationContext* opCtx, const boost::optional<TxnRecoveryToken>& recoveryToken);
/**
* Sends abort to all participants and returns the responses from all shards.
*/
std::vector<AsyncRequestsSender::Response> abortTransaction(OperationContext* opCtx,
bool isImplicit = false);
/**
* Sends abort to all shards in the current participant list. Will retry on retryable errors,
* but ignores the responses from each shard.
*/
void implicitlyAbortTransaction(OperationContext* opCtx, const Status& errorStatus);
/**
* Returns the participant for this transaction or nullptr if the specified shard is not
* participant of this transaction.
*/
Participant* getParticipant(const ShardId& shard);
/**
* If a coordinator has been selected for this transaction already, constructs a recovery token,
* which can be used to resume commit or abort of the transaction from a different router.
*/
void appendRecoveryToken(BSONObjBuilder* builder) const;
/**
* Returns a string with the active transaction's transaction number and logical session id
* (i.e. the transaction id).
*/
std::string txnIdToString() const;
/**
* Returns the statement id of the latest received command for this transaction.
*/
StmtId getLatestStmtId() const {
return _latestStmtId;
}
private:
// Shortcut to obtain the id of the session under which this transaction router runs
const LogicalSessionId& _sessionId() const;
/**
* Run basic commit for transactions that touched a single shard.
*/
Shard::CommandResponse _commitSingleShardTransaction(OperationContext* opCtx);
Shard::CommandResponse _commitWithRecoveryToken(OperationContext* opCtx,
const TxnRecoveryToken& recoveryToken);
/**
* Run two phase commit for transactions that touched multiple shards.
*/
Shard::CommandResponse _commitMultiShardTransaction(OperationContext* opCtx);
/**
* Sets the given logical time as the atClusterTime for the transaction to be the greater of the
* given time and the user's afterClusterTime, if one was provided.
*/
void _setAtClusterTime(const boost::optional<LogicalTime>& afterClusterTime,
LogicalTime candidateTime);
/**
* Throws NoSuchTransaction if the response from abortTransaction failed with a code other than
* NoSuchTransaction. Does not check for write concern errors.
*/
void _assertAbortStatusIsOkOrNoSuchTransaction(
const AsyncRequestsSender::Response& response) const;
/**
* Returns all participants created during the current statement.
*/
std::vector<ShardId> _getPendingParticipants() const;
/**
* Removes all participants created during the current statement from the participant list and
* sends abortTransaction to each. Waits for all responses before returning.
*/
void _clearPendingParticipants(OperationContext* opCtx);
/**
* Creates a new participant for the shard.
*/
Participant& _createParticipant(const ShardId& shard);
/**
* If the transaction's read concern level is snapshot, asserts the participant's atClusterTime
* matches the transaction's.
*/
void _verifyParticipantAtClusterTime(const Participant& participant);
// The currently active transaction number on this transaction router (i.e. on the session)
TxnNumber _txnNumber{kUninitializedTxnNumber};
// Whether the router has initiated a two-phase commit by handing off commit coordination to the
// coordinator. If so, the router should no longer implicitly abort the transaction on errors,
// since the coordinator may independently make a commit decision.
bool _initiatedTwoPhaseCommit{false};
// Indicates whether this is trying to recover a commitTransaction on the current transaction.
bool _isRecoveringCommit{false};
// Map of current participants of the current transaction.
StringMap<Participant> _participants;
// The id of coordinator participant, used to construct prepare requests.
boost::optional<ShardId> _coordinatorId;
// The read concern the current transaction was started with.
repl::ReadConcernArgs _readConcernArgs;
// The cluster time of the timestamp all participant shards in the current transaction with
// snapshot level read concern must read from. Only set for transactions running with snapshot
// level read concern.
boost::optional<AtClusterTime> _atClusterTime;
// The statement id of the latest received command for this transaction. For batch writes, this
// will be the highest stmtId contained in the batch. Incremented by one if new commands do not
// contain statement ids.
StmtId _latestStmtId = kUninitializedStmtId;
// The statement id of the command that began this transaction. Defaults to zero if no statement
// id was included in the first command.
StmtId _firstStmtId = kUninitializedStmtId;
};
} // namespace mongo
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