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/**
* Copyright (C) 2017 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 "mongo/base/disallow_copying.h"
#include "mongo/bson/timestamp.h"
#include "mongo/db/logical_session_id.h"
#include "mongo/db/repl/oplog_entry.h"
#include "mongo/db/session_txn_record_gen.h"
#include "mongo/stdx/unordered_map.h"
#include "mongo/util/concurrency/with_lock.h"
namespace mongo {
class OperationContext;
class UpdateRequest;
/**
* A write through cache for the state of a particular session. All modifications to the underlying
* session transactions collection must be performed through an object of this class.
*
* The cache state can be 'up-to-date' (it is in sync with the persistent contents) or 'needs
* refresh' (in which case refreshFromStorageIfNeeded needs to be called in order to make it
* up-to-date).
*/
class Session {
MONGO_DISALLOW_COPYING(Session);
public:
using CommittedStatementTimestampMap = stdx::unordered_map<StmtId, repl::OpTime>;
static const BSONObj kDeadEndSentinel;
explicit Session(LogicalSessionId sessionId);
const LogicalSessionId& getSessionId() const {
return _sessionId;
}
/**
* Blocking method, which loads the transaction state from storage if it has been marked as
* needing refresh.
*
* In order to avoid the possibility of deadlock, this method must not be called while holding a
* lock.
*/
void refreshFromStorageIfNeeded(OperationContext* opCtx);
/**
* Starts a new transaction on the session, must be called after refreshFromStorageIfNeeded has
* been called. If an attempt is made to start a transaction with number less than the latest
* transaction this session has seen, an exception will be thrown.
*
* Throws if the session has been invalidated or if an attempt is made to start a transaction
* older than the active.
*
* In order to avoid the possibility of deadlock, this method must not be called while holding a
* lock.
*/
void beginTxn(OperationContext* opCtx, TxnNumber txnNumber);
/**
* Called after a write under the specified transaction completes while the node is a primary
* and specifies the statement ids which were written. Must be called while the caller is still
* in the write's WUOW. Updates the on-disk state of the session to match the specified
* transaction/opTime and keeps the cached state in sync.
*
* Must only be called with the session checked-out.
*
* Throws if the session has been invalidated or the active transaction number doesn't match.
*/
void onWriteOpCompletedOnPrimary(OperationContext* opCtx,
TxnNumber txnNumber,
std::vector<StmtId> stmtIdsWritten,
const repl::OpTime& lastStmtIdWriteOpTime,
Date_t lastStmtIdWriteDate);
/**
* Called after an entry for the specified session and transaction has been written to the oplog
* during chunk migration, while the node is still primary. Must be called while the caller is
* still in the oplog write's WUOW. Updates the on-disk state of the session to match the
* specified transaction/opTime and keeps the cached state in sync.
*
* May be called concurrently with onWriteOpCompletedOnPrimary or onMigrateCompletedOnPrimary
* and doesn't require the session to be checked-out.
*
* Throws if the session has been invalidated or the active transaction number is newer than the
* one specified.
*/
void onMigrateCompletedOnPrimary(OperationContext* opCtx,
TxnNumber txnNumber,
std::vector<StmtId> stmtIdsWritten,
const repl::OpTime& lastStmtIdWriteOpTime,
Date_t lastStmtIdWriteDate);
/**
* Called after a replication batch has been applied on a secondary node. Keeps the session
* transaction entry in sync with the oplog chain which has been written.
*
* In order to avoid the possibility of deadlock, this method must not be called while holding a
* lock.
*/
static void updateSessionRecordOnSecondary(OperationContext* opCtx,
const SessionTxnRecord& sessionTxnRecord);
/**
* Marks the session as requiring refresh. Used when the session state has been modified
* externally, such as through a direct write to the transactions table.
*/
void invalidate();
/**
* Returns the op time of the last committed write for this session and transaction. If no write
* has completed yet, returns an empty timestamp.
*
* Throws if the session has been invalidated or the active transaction number doesn't match.
*/
repl::OpTime getLastWriteOpTime(TxnNumber txnNumber) const;
/**
* Checks whether the given statementId for the specified transaction has already executed and
* if so, returns the oplog entry which was generated by that write. If the statementId hasn't
* executed, returns boost::none.
*
* Must only be called with the session checked-out.
*
* Throws if the session has been invalidated or the active transaction number doesn't match.
*/
boost::optional<repl::OplogEntry> checkStatementExecuted(OperationContext* opCtx,
TxnNumber txnNumber,
StmtId stmtId) const;
/**
* Checks whether the given statementId for the specified transaction has already executed
* without fetching the oplog entry which was generated by that write.
*
* Must only be called with the session checked-out.
*
* Throws if the session has been invalidated or the active transaction number doesn't match.
*/
bool checkStatementExecutedNoOplogEntryFetch(TxnNumber txnNumber, StmtId stmtId) const;
private:
void _beginTxn(WithLock, TxnNumber txnNumber);
void _checkValid(WithLock) const;
void _checkIsActiveTransaction(WithLock, TxnNumber txnNumber) const;
boost::optional<repl::OpTime> _checkStatementExecuted(WithLock,
TxnNumber txnNumber,
StmtId stmtId) const;
UpdateRequest _makeUpdateRequest(WithLock,
TxnNumber newTxnNumber,
const repl::OpTime& newLastWriteTs,
Date_t newLastWriteDate) const;
void _registerUpdateCacheOnCommit(OperationContext* opCtx,
TxnNumber newTxnNumber,
std::vector<StmtId> stmtIdsWritten,
const repl::OpTime& lastStmtIdWriteTs);
const LogicalSessionId _sessionId;
// Protects the member variables below.
mutable stdx::mutex _mutex;
// Specifies whether the session information needs to be refreshed from storage
bool _isValid{false};
// Counter, incremented with each call to invalidate in order to discern invalidations, which
// happen during refresh
int _numInvalidations{0};
// Set to true if incomplete history is detected. For example, when the oplog to a write was
// truncated because it was too old.
bool _hasIncompleteHistory{false};
// Caches what is known to be the last written transaction record for the session
boost::optional<SessionTxnRecord> _lastWrittenSessionRecord;
// Tracks the last seen txn number for the session and is always >= to the transaction number in
// the last written txn record. When it is > than that in the last written txn record, this
// means a new transaction has begun on the session, but it hasn't yet performed any writes.
TxnNumber _activeTxnNumber{kUninitializedTxnNumber};
// For the active txn, tracks which statement ids have been committed and at which oplog
// opTime. Used for fast retryability check and retrieving the previous write's data without
// having to scan through the oplog.
CommittedStatementTimestampMap _activeTxnCommittedStatements;
};
} // namespace mongo
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