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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 <list>
#include <string>
#include <unordered_map>
#include "mongo/bson/timestamp.h"
#include "mongo/db/namespace_string.h"
#include "mongo/db/operation_context.h"
#include "mongo/db/service_context.h"
#include "mongo/platform/mutex.h"
#include "mongo/util/uuid.h"
namespace mongo {
/**
* Keeps track of historical ident information when a collection is renamed or dropped.
*/
class HistoricalIdentTracker final {
public:
HistoricalIdentTracker(const HistoricalIdentTracker&) = delete;
HistoricalIdentTracker(HistoricalIdentTracker&&) = delete;
static HistoricalIdentTracker& get(ServiceContext* svcCtx);
static HistoricalIdentTracker& get(OperationContext* opCtx);
HistoricalIdentTracker() = default;
~HistoricalIdentTracker() = default;
/**
* Returns the historical namespace and UUID for 'ident' at 'timestamp'. Returns boost::none if
* there was no historical namespace.
*/
boost::optional<std::pair<NamespaceString, UUID>> lookup(const std::string& ident,
Timestamp timestamp) const;
/**
* Pins the historical content to the given timestamp, preventing it from being removed.
*
* This is necessary for backup cursors, which need to report the namespace and UUID at the time
* of the checkpoint the backup is being taken on. When a backup cursor is open, it pins the
* checkpoint the backup is being taken on. Checkpoints can still be taken, which advances the
* last checkpoint timestamp and would remove historical content needed by the open backup
* cursor. This method prevents that from happening by pinning the content.
*
* The checkpoint timestamp of the backup can be earlier than the oldest timestamp, which
* prevents us from opening a snapshot at the checkpoint timestamp as history before the oldest
* timestamp is discarded.
*/
void pinAtTimestamp(Timestamp timestamp);
void unpin();
/**
* Records the idents namespace and UUID before it was renamed.
*/
void recordRename(const std::string& ident,
const NamespaceString& oldNss,
const UUID& uuid,
Timestamp timestamp) {
_addHistoricalIdent(ident, oldNss, uuid, timestamp);
}
/**
* Records the idents namespace and UUID before it was dropped.
*/
void recordDrop(const std::string& ident,
const NamespaceString& nss,
const UUID& uuid,
Timestamp timestamp) {
_addHistoricalIdent(ident, nss, uuid, timestamp);
}
/**
* Removes historical content that is no longer necessary. This is anything older than the last
* checkpoint timestamp.
*
* If there's a pinned timestamp, min(timestamp, _pinnedTimestamp) is used.
*/
void removeEntriesOlderThan(Timestamp timestamp);
/**
* Historical content added may not be stable yet and can be rolled back. When rollback to
* stable runs, we need to remove any historical content that is considered current.
*
* If there's a pinned timestamp, max(timestamp, _pinnedTimestamp) is used.
*/
void rollbackTo(Timestamp timestamp);
private:
/**
* Helper function for recordRename() and recordDrop().
*
* Appends a new historical entry with 'nss' and 'uuid' for 'ident' in '_historicalIdents'.
* Sets the 'end' timestamp to be 'timestamp - 1'.
* Sets the 'start' timestamp to the timestamp of the last entry + 1, or Timestamp::min() if
* there was no earlier entry.
*/
void _addHistoricalIdent(const std::string& ident,
const NamespaceString& nss,
const UUID& uuid,
Timestamp timestamp);
struct HistoricalIdentEntry {
const NamespaceString nss;
const UUID uuid;
Timestamp start;
Timestamp end;
};
// Protects all the member variables below.
mutable Mutex _mutex = MONGO_MAKE_LATCH("HistoricalIdentTracker::_mutex");
stdx::unordered_map<std::string, std::list<HistoricalIdentEntry>> _historicalIdents;
Timestamp _pinnedTimestamp;
};
} // namespace mongo
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