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/**
* Copyright (C) 2022-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 "mongo/db/session/internal_session_pool.h"
#include "mongo/db/session/logical_session_id.h"
#include <vector>
namespace mongo {
namespace repl {
using PooledSession = InternalSessionPool::Session;
/**
* This struct contains information for a split session, including the split
* session itself and the id of the requester who wants to acquire the split
* session, which is usually a writer thread from the oplog applier.
*/
struct SplitSessionInfo {
PooledSession session;
uint32_t requesterId;
SplitSessionInfo(PooledSession&& sess, uint32_t reqId)
: session(std::move(sess)), requesterId(reqId) {}
};
/**
* This class manages the sessions for split prepared transactions.
*
* Prepared transactions are split and applied in parallel on secondaries, and this class is
* used to create split sessions and track the mapping of top-level sessions and their splits.
* A primary can also see prepared transactions in the split state if it performed the split
* and prepare without committing when it was still a secondary, so this class can be accessed
* by both primaries and secondaries.
*/
class SplitPrepareSessionManager {
SplitPrepareSessionManager(const SplitPrepareSessionManager&) = delete;
SplitPrepareSessionManager& operator=(const SplitPrepareSessionManager&) = delete;
public:
explicit SplitPrepareSessionManager(InternalSessionPool* sessionPool);
/**
* Creates split sessions for the given top-level session and track the mapping.
*
* The txnNumber is the txnNumber of the top-level session that needs to be split. It
* servers as a sanity check: onces a session is split, it can not be split again for
* another txnNumber until it releases the existing split sessions.
*
* The requesterIds is a sorted list of requesters (usually writer threads from the
* oplog applier), each of whom wants to acquire a split session.
*
* Asserts if the given session is already split.
*/
const std::vector<SplitSessionInfo>& splitSession(const LogicalSessionId& sessionId,
TxnNumber txnNumber,
const std::vector<uint32_t>& requesterIds);
/**
* Returns a vector of split sessions for the given top-level session, or nothing if
* the given session has not been split.
*
* The txnNumber servers a sanity check to make sure it is the same as the one being
* used for splitSession().
*/
boost::optional<const std::vector<SplitSessionInfo>&> getSplitSessions(
const LogicalSessionId& sessionId, TxnNumber txnNumber) const;
/**
* Returns true if the given session has been split, or false otherwise. This can be
* used as an alternative to getSplitSessionIds() when the result is not needed.
*
* The txnNumber servers a sanity check to make sure it is the same as the one being
* used for splitSession().
*/
bool isSessionSplit(const LogicalSessionId& sessionId, TxnNumber txnNumber) const;
/**
* Releases all the split sessions of the give top-level session into the session pool
* and stops tracking their mapping.
*
* The txnNumber servers a sanity check to make sure it is the same as the one being
* used for splitSession().
*
* Asserts if the given session is not split.
*/
void releaseSplitSessions(const LogicalSessionId& sessionId, TxnNumber txnNumber);
/**
* Release and remove all the tracked split sessions.
*/
void releaseAllSplitSessions();
private:
// Guards access to member variables.
mutable Mutex _mutex = MONGO_MAKE_LATCH("SplitPrepareSessionManager::_mutex");
// The global session pool storing reusable sessions, from which split sessions are acquired.
InternalSessionPool* _sessionPool;
// A map to track top-level sessions and their splits.
LogicalSessionIdMap<std::pair<TxnNumber, std::vector<SplitSessionInfo>>> _splitSessionMap;
};
} // namespace repl
} // namespace mongo
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