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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 "mongo/db/storage/wiredtiger/wiredtiger_record_store.h"
#include "mongo/platform/mutex.h"
#include "mongo/stdx/condition_variable.h"
#include "mongo/stdx/thread.h"
#include "mongo/util/concurrency/with_lock.h"
namespace mongo {
class WiredTigerRecordStore;
class WiredTigerSessionCache;
// Manages oplog visibility, by periodically querying WiredTiger's all_durable timestamp value and
// then using that timestamp for all transactions that read the oplog collection.
class WiredTigerOplogManager {
WiredTigerOplogManager(const WiredTigerOplogManager&) = delete;
WiredTigerOplogManager& operator=(const WiredTigerOplogManager&) = delete;
public:
WiredTigerOplogManager() {}
~WiredTigerOplogManager() {}
// This method will initialize the oplog read timestamp and start the background thread that
// refreshes the value.
void start(OperationContext* opCtx,
const std::string& uri,
WiredTigerRecordStore* oplogRecordStore);
void halt();
bool isRunning() {
stdx::lock_guard<Latch> lk(_oplogVisibilityStateMutex);
return _isRunning && !_shuttingDown;
}
// The oplogReadTimestamp is the timestamp used for oplog reads, to prevent readers from
// reading past uncommitted transactions (which may create "holes" in the oplog after an
// unclean shutdown).
std::uint64_t getOplogReadTimestamp() const;
void setOplogReadTimestamp(Timestamp ts);
// Triggers the oplogJournal thread to update its oplog read timestamp, by flushing the journal.
void triggerJournalFlush();
// Waits until all committed writes at this point to become visible (that is, no holes exist in
// the oplog.)
void waitForAllEarlierOplogWritesToBeVisible(const WiredTigerRecordStore* oplogRecordStore,
OperationContext* opCtx);
private:
void _oplogJournalThreadLoop(WiredTigerSessionCache* sessionCache,
WiredTigerRecordStore* oplogRecordStore);
void _setOplogReadTimestamp(WithLock, uint64_t newTimestamp);
stdx::thread _oplogJournalThread;
mutable Mutex _oplogVisibilityStateMutex =
MONGO_MAKE_LATCH("WiredTigerOplogManager::_oplogVisibilityStateMutex");
mutable stdx::condition_variable
_opsWaitingForJournalCV; // Signaled to trigger a journal flush.
mutable stdx::condition_variable
_opsBecameVisibleCV; // Signaled when a journal flush is complete.
bool _isRunning = false; // Guarded by oplogVisibilityStateMutex.
bool _shuttingDown = false; // Guarded by oplogVisibilityStateMutex.
bool _opsWaitingForJournal = false; // Guarded by oplogVisibilityStateMutex.
// When greater than 0, indicates that there are operations waiting for oplog visibility, and
// journal flushing should not be delayed.
std::int64_t _opsWaitingForVisibility = 0; // Guarded by oplogVisibilityStateMutex.
AtomicWord<unsigned long long> _oplogReadTimestamp{0};
};
} // namespace mongo
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