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/*
* Copyright (C) 2018 MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* 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
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* 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 GNU Affero General 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 <iostream>
#include <map>
#include "mongo/base/disallow_copying.h"
#include "mongo/db/concurrency/locker.h"
#include "mongo/db/logical_session_id.h"
#include "mongo/db/multi_key_path_tracker.h"
#include "mongo/db/repl/oplog.h"
#include "mongo/db/repl/read_concern_args.h"
#include "mongo/db/session.h"
#include "mongo/db/single_transaction_stats.h"
#include "mongo/db/storage/recovery_unit.h"
#include "mongo/util/assert_util.h"
#include "mongo/util/concurrency/with_lock.h"
#include "mongo/util/decorable.h"
#include "mongo/util/mongoutils/str.h"
namespace mongo {
class OperationContext;
extern AtomicInt32 transactionLifetimeLimitSeconds;
/**
* A state machine that coordinates a distributed transaction commit with the transaction
* coordinator.
*/
class TransactionParticipant {
MONGO_DISALLOW_COPYING(TransactionParticipant);
public:
/**
* Holds state for a snapshot read or multi-statement transaction in between network
* operations.
*/
class TxnResources {
public:
/**
* Stashes transaction state from 'opCtx' in the newly constructed TxnResources.
*/
TxnResources(OperationContext* opCtx, bool keepTicket = false);
~TxnResources();
// Rule of 5: because we have a class-defined destructor, we need to explictly specify
// the move operator and move assignment operator.
TxnResources(TxnResources&&) = default;
TxnResources& operator=(TxnResources&&) = default;
/**
* Returns a const pointer to the stashed lock state, or nullptr if no stashed locks exist.
*/
const Locker* locker() const {
return _locker.get();
}
/**
* Releases stashed transaction state onto 'opCtx'. Must only be called once.
*/
void release(OperationContext* opCtx);
/**
* Returns the read concern arguments.
*/
repl::ReadConcernArgs getReadConcernArgs() const {
return _readConcernArgs;
}
private:
bool _released = false;
std::unique_ptr<Locker> _locker;
std::unique_ptr<RecoveryUnit> _recoveryUnit;
repl::ReadConcernArgs _readConcernArgs;
WriteUnitOfWork::RecoveryUnitState _ruState;
};
/**
* An RAII object that stashes `TxnResouces` from the `opCtx` onto the stack. At destruction
* it unstashes the `TxnResources` back onto the `opCtx`.
*/
class SideTransactionBlock {
public:
SideTransactionBlock(OperationContext* opCtx);
~SideTransactionBlock();
// Rule of 5: because we have a class-defined destructor, we need to explictly specify
// the move operator and move assignment operator.
SideTransactionBlock(SideTransactionBlock&&) = default;
SideTransactionBlock& operator=(SideTransactionBlock&&) = default;
private:
boost::optional<TxnResources> _txnResources;
OperationContext* _opCtx;
};
static TransactionParticipant* get(OperationContext* opCtx);
/**
* This should only be used when session was obtained without checking it out.
*/
static TransactionParticipant* getFromNonCheckedOutSession(Session* session);
TransactionParticipant() = default;
static boost::optional<TransactionParticipant>& get(Session* session);
static void create(Session* session);
class StateMachine {
public:
friend class TransactionParticipant;
// Note: We must differentiate the 'committed/aborted' and 'committed/aborted after prepare'
// states, because it is illegal to receive, for example, a prepare request after a
// commit/abort if no prepare was received before the commit/abort.
enum class State {
kUnprepared,
kAborted,
kCommitted,
kWaitingForDecision,
kAbortedAfterPrepare,
kCommittedAfterPrepare,
// The state machine transitions to this state when a message that is considered illegal
// to receive in a particular state is received. This indicates either a byzantine
// message, or that the transition table does not accurately reflect an asynchronous
// network.
kBroken,
};
// State machine inputs
enum class Event {
kRecvPrepare,
kVoteCommitRejected,
kRecvAbort,
kRecvCommit,
};
// State machine outputs
enum class Action {
kNone,
kPrepare,
kAbort,
kCommit,
kSendCommitAck,
kSendAbortAck,
};
Action onEvent(Event e);
State state() {
return _state;
}
private:
struct Transition {
Transition() : action(Action::kNone) {}
Transition(Action action) : action(action) {}
Transition(Action action, State state) : action(action), nextState(state) {}
Action action;
boost::optional<State> nextState;
};
static const std::map<State, std::map<Event, Transition>> transitionTable;
State _state{State::kUnprepared};
};
/**
* Called for speculative transactions to fix the optime of the snapshot to read from.
*/
void setSpeculativeTransactionOpTimeToLastApplied(OperationContext* opCtx);
/**
* Transfers management of transaction resources from the OperationContext to the Session.
*/
void stashTransactionResources(OperationContext* opCtx);
/**
* Transfers management of transaction resources from the Session to the OperationContext.
*/
void unstashTransactionResources(OperationContext* opCtx, const std::string& cmdName);
/**
* Commits the transaction, including committing the write unit of work and updating
* transaction state.
*
* Throws an exception if the transaction is prepared.
*/
void commitUnpreparedTransaction(OperationContext* opCtx);
/**
* Commits the transaction, including committing the write unit of work and updating
* transaction state.
*
* Throws an exception if the transaction is not prepared or if the 'commitTimestamp' is null.
*/
void commitPreparedTransaction(OperationContext* opCtx, Timestamp commitTimestamp);
/**
* Puts a transaction into a prepared state and returns the prepareTimestamp.
*/
Timestamp prepareTransaction(OperationContext* opCtx);
/**
* Returns whether we are in a multi-document transaction, which means we have an active
* transaction which has autoCommit:false and has not been committed or aborted. It is possible
* that the current transaction is stashed onto the stack via a `SideTransactionBlock`.
*/
bool inMultiDocumentTransaction() const {
stdx::lock_guard<stdx::mutex> lk(_mutex);
return _txnState.inMultiDocumentTransaction(lk);
};
bool transactionIsCommitted() const {
stdx::lock_guard<stdx::mutex> lk(_mutex);
return _txnState.isCommitted(lk);
}
bool transactionIsAborted() const {
stdx::lock_guard<stdx::mutex> lk(_mutex);
return _txnState.isAborted(lk);
}
/**
* Adds a stored operation to the list of stored operations for the current multi-document
* (non-autocommit) transaction. It is illegal to add operations when no multi-document
* transaction is in progress.
*/
void addTransactionOperation(OperationContext* opCtx, const repl::ReplOperation& operation);
/**
* Returns and clears the stored operations for an multi-document (non-autocommit) transaction,
* and marks the transaction as closed. It is illegal to attempt to add operations to the
* transaction after this is called.
*/
std::vector<repl::ReplOperation> endTransactionAndRetrieveOperations(OperationContext* opCtx);
const std::vector<repl::ReplOperation>& transactionOperationsForTest() {
return _transactionOperations;
}
SingleTransactionStats getSingleTransactionStats() const {
return _singleTransactionStats;
}
repl::OpTime getSpeculativeTransactionReadOpTimeForTest() const {
stdx::lock_guard<stdx::mutex> lk(_mutex);
return _speculativeTransactionReadOpTime;
}
const Locker* getTxnResourceStashLockerForTest() const {
stdx::lock_guard<stdx::mutex> lk(_mutex);
invariant(_txnResourceStash);
return _txnResourceStash->locker();
}
/**
* If this session is holding stashed locks in _txnResourceStash, reports the current state of
* the session using the provided builder. Locks the session object's mutex while running.
*/
void reportStashedState(BSONObjBuilder* builder) const;
std::string transactionInfoForLogForTest(const SingleThreadedLockStats* lockStats,
bool committed,
repl::ReadConcernArgs readConcernArgs) {
stdx::lock_guard<stdx::mutex> lk(_mutex);
TransactionState::StateFlag terminationCause =
committed ? TransactionState::kCommitted : TransactionState::kAborted;
return _transactionInfoForLog(lockStats, terminationCause, readConcernArgs);
}
/**
* If this session is not holding stashed locks in _txnResourceStash (transaction is active),
* reports the current state of the session using the provided builder. Locks the session
* object's mutex while running.
*/
void reportUnstashedState(repl::ReadConcernArgs readConcernArgs, BSONObjBuilder* builder) const;
/**
* Convenience method which creates and populates a BSONObj containing the stashed state.
* Returns an empty BSONObj if this session has no stashed resources.
*/
BSONObj reportStashedState() const;
/**
* Aborts the transaction outside the transaction, releasing transaction resources.
*
* Not called with session checked out.
*/
void abortArbitraryTransaction();
/**
* Same as abortArbitraryTransaction, except only executes if _transactionExpireDate indicates
* that the transaction has expired.
*
* Not called with session checked out.
*/
void abortArbitraryTransactionIfExpired();
/*
* Aborts the transaction inside the transaction, releasing transaction resources.
* We're inside the transaction when we have the Session checked out and 'opCtx' owns the
* transaction resources.
* Aborts the transaction and releases transaction resources when we have the Session checked
* out and 'opCtx' owns the transaction resources.
*/
void abortActiveTransaction(OperationContext* opCtx);
/*
* If the transaction is prepared, stash its resources. If not, it's the same as
* abortActiveTransaction.
*/
void abortActiveUnpreparedOrStashPreparedTransaction(OperationContext* opCtx);
void addMultikeyPathInfo(MultikeyPathInfo info) {
_multikeyPathInfo.push_back(std::move(info));
}
const std::vector<MultikeyPathInfo>& getMultikeyPathInfo() const {
return _multikeyPathInfo;
}
/**
* Starts a new transaction, or continues an already active transaction.
*
* The 'autocommit' argument represents the value of the field given in the original client
* request. If it is boost::none, no autocommit parameter was passed into the request. Every
* operation that is part of a multi statement transaction must specify 'autocommit=false'.
* 'startTransaction' represents the value of the field given in the original client request,
* and indicates whether this operation is the beginning of a multi-statement transaction.
*
* Throws an exception if:
* - The values of 'autocommit' and/or 'startTransaction' are inconsistent with the current
* state of the transaction.
*/
void beginOrContinue(TxnNumber txnNumber,
boost::optional<bool> autocommit,
boost::optional<bool> startTransaction);
static Status isValid(StringData dbName, StringData cmdName);
void transitionToPreparedforTest() {
stdx::lock_guard<stdx::mutex> lk(_mutex);
_txnState.transitionTo(lk, TransactionState::kPrepared);
}
void transitionToCommittingforTest() {
stdx::lock_guard<stdx::mutex> lk(_mutex);
_txnState.transitionTo(lk, TransactionState::kCommittingWithoutPrepare);
}
/**
* Checks to see if the txnNumber changed in the parent session and perform the necessary
* cleanup.
*/
void checkForNewTxnNumber();
private:
/**
* Reserves a slot in the oplog with an open storage-transaction while it is alive. Reserves the
* slot at construction. Aborts the storage-transaction and releases the oplog slot at
* destruction.
*/
class OplogSlotReserver {
public:
OplogSlotReserver(OperationContext* opCtx);
~OplogSlotReserver();
// Rule of 5: because we have a class-defined destructor, we need to explictly specify
// the move operator and move assignment operator.
OplogSlotReserver(OplogSlotReserver&&) = default;
OplogSlotReserver& operator=(OplogSlotReserver&&) = default;
/**
* Returns the oplog slot reserved at construction.
*/
OplogSlot getReservedOplogSlot() const {
invariant(!_oplogSlot.opTime.isNull());
return _oplogSlot;
}
private:
std::unique_ptr<Locker> _locker;
std::unique_ptr<RecoveryUnit> _recoveryUnit;
OplogSlot _oplogSlot;
};
/**
* Indicates the state of the current multi-document transaction, if any. If the transaction is
* in any state but kInProgress, no more operations can be collected. Once the transaction is in
* kPrepared, the transaction is not allowed to abort outside of an 'abortTransaction' command.
* At this point, aborting the transaction must log an 'abortTransaction' oplog entry.
*/
class TransactionState {
public:
enum StateFlag {
kNone = 1 << 0,
kInProgress = 1 << 1,
kPrepared = 1 << 2,
kCommittingWithoutPrepare = 1 << 3,
kCommittingWithPrepare = 1 << 4,
kCommitted = 1 << 5,
kAborted = 1 << 6
};
using StateSet = int;
bool isInSet(WithLock, StateSet stateSet) const {
return _state & stateSet;
}
/**
* Transitions the session from the current state to the new state. If transition validation
* is not relaxed, invariants if the transition is illegal.
*/
enum class TransitionValidation { kValidateTransition, kRelaxTransitionValidation };
void transitionTo(
WithLock,
StateFlag newState,
TransitionValidation shouldValidate = TransitionValidation::kValidateTransition);
bool inMultiDocumentTransaction(WithLock) const {
return _state == kInProgress || _state == kPrepared;
}
bool isNone(WithLock) const {
return _state == kNone;
}
bool isInProgress(WithLock) const {
return _state == kInProgress;
}
bool isPrepared(WithLock) const {
return _state == kPrepared;
}
bool isCommittingWithoutPrepare(WithLock) const {
return _state == kCommittingWithoutPrepare;
}
bool isCommittingWithPrepare(WithLock) const {
return _state == kCommittingWithPrepare;
}
bool isCommitted(WithLock) const {
return _state == kCommitted;
}
bool isAborted(WithLock) const {
return _state == kAborted;
}
std::string toString() const {
return toString(_state);
}
static std::string toString(StateFlag state);
private:
static bool _isLegalTransition(StateFlag oldState, StateFlag newState);
StateFlag _state = kNone;
};
friend std::ostream& operator<<(std::ostream& s, TransactionState txnState) {
return (s << txnState.toString());
}
friend StringBuilder& operator<<(StringBuilder& s, TransactionState txnState) {
return (s << txnState.toString());
}
// Committing a transaction first changes its state to "Committing*" and writes to the oplog,
// then it changes the state to "Committed".
//
// When a transaction is in "Committing" state, it's not allowed for other threads to change
// its state (i.e. abort the transaction), otherwise the on-disk state will diverge from the
// in-memory state.
// There are 3 cases where the transaction will be aborted.
// 1) abortTransaction command. Session check-out mechanism only allows one client to access a
// transaction.
// 2) killSession, stepdown, transaction timeout and any thread that aborts the transaction
// outside of session checkout. They can safely skip the committing transactions.
// 3) Migration. Should be able to skip committing transactions.
void _commitTransaction(stdx::unique_lock<stdx::mutex> lk, OperationContext* opCtx);
// Stash transaction resources.
void _stashActiveTransaction(WithLock, OperationContext* opCtx);
// Abort the transaction if it's in one of the expected states and clean up the transaction
// states associated with the opCtx.
void _abortActiveTransaction(WithLock,
OperationContext* opCtx,
TransactionState::StateSet expectedStates);
void _abortArbitraryTransaction(WithLock);
// Releases stashed transaction resources to abort the transaction on the session.
void _abortTransactionOnSession(WithLock);
// Clean up the transaction resources unstashed on operation context.
void _cleanUpTxnResourceOnOpCtx(WithLock wl, OperationContext* opCtx);
// Checks if the current transaction number of this transaction still matches with the
// parent session as well as the transaction number of the current operation context.
void _checkIsActiveTransaction(WithLock,
const TxnNumber& requestTxnNumber,
bool checkAbort) const;
// Logs the transaction information if it has run slower than the global parameter slowMS. The
// transaction must be committed or aborted when this function is called.
void _logSlowTransaction(WithLock wl,
const SingleThreadedLockStats* lockStats,
TransactionState::StateFlag terminationCause,
repl::ReadConcernArgs readConcernArgs);
// This method returns a string with information about a slow transaction. The format of the
// logging string produced should match the format used for slow operation logging. A
// transaction must be completed (committed or aborted) and a valid LockStats reference must be
// passed in order for this method to be called.
std::string _transactionInfoForLog(const SingleThreadedLockStats* lockStats,
TransactionState::StateFlag terminationCause,
repl::ReadConcernArgs readConcernArgs);
// Reports transaction stats for both active and inactive transactions using the provided
// builder.
void _reportTransactionStats(WithLock wl,
BSONObjBuilder* builder,
repl::ReadConcernArgs readConcernArgs) const;
void _updateState(WithLock wl, const Session::RefreshState& newState);
// Bumps up the transaction number of this transaction and perform the necessary cleanup.
void _setNewTxnNumber(WithLock wl, const TxnNumber& txnNumber);
// Returns the session that this transaction belongs to.
const Session* _getSession() const;
Session* _getSession();
// Protects the member variables below.
mutable stdx::mutex _mutex;
// Holds transaction resources between network operations.
boost::optional<TxnResources> _txnResourceStash;
// Maintains the transaction state and the transition table for legal state transitions.
TransactionState _txnState;
StateMachine _stateMachine;
// Holds oplog data for operations which have been applied in the current multi-document
// transaction.
std::vector<repl::ReplOperation> _transactionOperations;
// Total size in bytes of all operations within the _transactionOperations vector.
size_t _transactionOperationBytes = 0;
// This is the txnNumber that this transaction is actively working on. It can be different from
// the current txnNumber of the parent session (since it can be changed in couple of ways, like
// migration). In which case, it should make the necessary steps to also bump this number, like
// aborting the current transaction.
TxnNumber _activeTxnNumber{kUninitializedTxnNumber};
// Set when a snapshot read / transaction begins. Alleviates cache pressure by limiting how long
// a snapshot will remain open and available. Checked in combination with _txnState to determine
// whether the transaction should be aborted.
// This is unset until a transaction begins on the session, and then reset only when new
// transactions begin.
boost::optional<Date_t> _transactionExpireDate;
// The autoCommit setting of this transaction. Should always be false for multi-statement
// transaction. Currently only needed for diagnostics reporting.
boost::optional<bool> _autoCommit;
// The OpTime a speculative transaction is reading from and also the earliest opTime it
// should wait for write concern for on commit.
repl::OpTime _speculativeTransactionReadOpTime;
std::vector<MultikeyPathInfo> _multikeyPathInfo;
// Tracks metrics for a single multi-document transaction.
SingleTransactionStats _singleTransactionStats;
// Remembers the refresh count this object has read from Session.
long long _lastStateRefreshCount{0};
};
inline StringBuilder& operator<<(StringBuilder& sb,
const TransactionParticipant::StateMachine::State& state) {
using State = TransactionParticipant::StateMachine::State;
switch (state) {
// clang-format off
case State::kUnprepared: return sb << "Unprepared";
case State::kAborted: return sb << "Aborted";
case State::kCommitted: return sb << "Committed";
case State::kWaitingForDecision: return sb << "WaitingForDecision";
case State::kAbortedAfterPrepare: return sb << "AbortedAfterPrepare";
case State::kCommittedAfterPrepare: return sb << "CommittedAfterPrepare";
case State::kBroken: return sb << "Broken";
// clang-format on
default:
MONGO_UNREACHABLE;
};
}
inline std::ostream& operator<<(std::ostream& os,
const TransactionParticipant::StateMachine::State& state) {
StringBuilder sb;
sb << state;
return os << sb.str();
}
inline StringBuilder& operator<<(StringBuilder& sb,
const TransactionParticipant::StateMachine::Event& event) {
using Event = TransactionParticipant::StateMachine::Event;
switch (event) {
// clang-format off
case Event::kRecvPrepare: return sb << "RecvPrepare";
case Event::kVoteCommitRejected: return sb << "VoteCommitRejected";
case Event::kRecvAbort: return sb << "RecvAbort";
case Event::kRecvCommit: return sb << "RecvCommit";
// clang-format on
default:
MONGO_UNREACHABLE;
};
}
inline std::ostream& operator<<(std::ostream& os,
const TransactionParticipant::StateMachine::Event& event) {
StringBuilder sb;
sb << event;
return os << sb.str();
}
inline StringBuilder& operator<<(StringBuilder& sb,
const TransactionParticipant::StateMachine::Action& action) {
using Action = TransactionParticipant::StateMachine::Action;
switch (action) {
// clang-format off
case Action::kNone: return sb << "None";
case Action::kPrepare: return sb << "Prepare";
case Action::kAbort: return sb << "Abort";
case Action::kCommit: return sb << "Commit";
case Action::kSendCommitAck: return sb << "SendCommitAck";
case Action::kSendAbortAck: return sb << "SendAbortAck";
// clang-format on
default:
MONGO_UNREACHABLE;
};
}
inline std::ostream& operator<<(std::ostream& os,
const TransactionParticipant::StateMachine::Action& action) {
StringBuilder sb;
sb << action;
return os << sb.str();
}
} // namespace mongo
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