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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 <limits>
#include <string>
#include "mongo/base/status.h"
#include "mongo/bson/timestamp.h"
#include "mongo/db/operation_context.h"
#include "mongo/util/assert_util.h"
namespace mongo {
class RecoveryUnit;
/**
* Manages snapshots that can be read from at a later time.
*
* Implementations must be able to handle concurrent access to any methods. No methods are allowed
* to acquire locks from the LockManager.
*/
class SnapshotManager {
public:
/**
* Prepares the passed-in OperationContext for snapshot creation.
*
* The passed-in OperationContext will be associated with a point-in-time that can be used
* for creating a snapshot later.
*
* This must be the first method called after starting a ScopedTransaction, and it is
* illegal to start a WriteUnitOfWork inside of the same ScopedTransaction.
*/
virtual Status prepareForCreateSnapshot(OperationContext* opCtx) = 0;
/**
* Sets the snapshot to be used for committed reads.
*
* Implementations are allowed to assume that all older snapshots have names that compare
* less than the passed in name, and newer ones compare greater.
*
* This is called while holding a very hot mutex. Therefore it should avoid doing any work that
* can be done later. In particular, cleaning up of old snapshots should be deferred until
* cleanupUnneededSnapshots is called.
*/
virtual void setCommittedSnapshot(const Timestamp& timestamp) = 0;
/**
* Cleans up all snapshots older than the current committed snapshot.
*
* Operations that have already begun using an older snapshot must continue to work using that
* snapshot until they would normally start using a newer one. Any implementation that allows
* that without an unbounded growth of snapshots is permitted.
*/
virtual void cleanupUnneededSnapshots() = 0;
/**
* Drops all snapshots and clears the "committed" snapshot.
*/
virtual void dropAllSnapshots() = 0;
protected:
/**
* SnapshotManagers are not intended to be deleted through pointers to base type.
* (virtual is just to suppress compiler warnings)
*/
virtual ~SnapshotManager() = default;
};
} // namespace mongo
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