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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 <boost/optional.hpp>
#include <map>
#include <set>
#include <string>
#include "mongo/base/string_data.h"
#include "mongo/bson/timestamp.h"
#include "mongo/db/namespace_string.h"
#include "mongo/db/storage/kv/kv_engine.h"
#include "mongo/platform/mutex.h"
namespace mongo {
class Ident;
/**
* This class manages idents in the KV storage engine that are marked as drop-pending by the
* two-phase index/collection drop algorithm.
*
* Replicated collections and indexes that are dropped are not permanently removed from the storage
* system when the drop request is first processed. The catalog entry is removed to render the
* collection or index inaccessible to user operations but the underlying ident is retained in the
* event we have to recover the collection. This is relevant mostly to rollback and startup
* recovery.
*
* On receiving a notification that the oldest timestamp queued has advanced and become part of the
* checkpoint, some drop-pending idents will become safe to remove permanently. The function
* dropldentsOlderThan() is provided for this purpose.
*
* Additionally, the reaper will not drop an ident (record store) while any other references to the
* Ident passed in via addDropPendingIdent remain. This ensures that there are no remaining
* concurrent operations still using the record store, which is essential because a data drop is
* unversioned: once it is dropped, it is gone for all readers.
*/
class KVDropPendingIdentReaper {
KVDropPendingIdentReaper(const KVDropPendingIdentReaper&) = delete;
KVDropPendingIdentReaper& operator=(const KVDropPendingIdentReaper&) = delete;
public:
explicit KVDropPendingIdentReaper(KVEngine* engine);
virtual ~KVDropPendingIdentReaper() = default;
/**
* Adds a new drop-pending ident, with its drop timestamp and namespace, to be managed by this
* class.
*
* When the timestamp is old enough -- the op cannot be rolled back nor new users access the
* record store data -- and no remaining operations reference the 'ident', then the
* index/collection data will be safe to drop unversioned.
*/
void addDropPendingIdent(const Timestamp& dropTimestamp,
const NamespaceString& nss,
std::shared_ptr<Ident> ident,
StorageEngine::DropIdentCallback&& onDrop = nullptr);
/**
* Returns earliest drop timestamp in '_dropPendingIdents'.
* Returns boost::none if '_dropPendingIdents' is empty.
*/
boost::optional<Timestamp> getEarliestDropTimestamp() const;
/**
* Returns drop-pending idents in a sorted set.
* Used by the storage engine during catalog reconciliation.
*/
std::set<std::string> getAllIdentNames() const;
/**
* Notifies this class that the storage engine has advanced its oldest timestamp.
* Drops all unreferenced drop-pending idents with drop timestamps before 'ts', as well as all
* unreferenced idents with Timestamp::min() drop timestamps (untimestamped on standalones).
*/
void dropIdentsOlderThan(OperationContext* opCtx, const Timestamp& ts);
/**
* Clears maps of drop pending idents but does not drop idents in storage engine.
* Used by rollback after recovering to a stable timestamp.
*/
void clearDropPendingState();
private:
// Contains information identifying what collection/index data to drop as well as determining
// when to do so.
using IdentInfo = struct {
// Used for logging purposes.
NamespaceString nss;
// Identifier for the storage to drop the associated collection or index data.
std::string identName;
// The collection or index data can be safely dropped when no references to this token
// remain.
std::weak_ptr<void> dropToken;
// Callback to run once the ident has been dropped.
StorageEngine::DropIdentCallback onDrop;
};
// Container type for drop-pending namespaces. We use a multimap so that we can order the
// namespaces by drop optime. Additionally, it is possible for certain user operations (such
// as renameCollection across databases) to generate more than one drop-pending namespace for
// the same drop optime.
using DropPendingIdents = std::multimap<Timestamp, IdentInfo>;
// Used to access the KV engine for the purposes of dropping the ident.
KVEngine* const _engine;
// Guards access to member variables below.
mutable Mutex _mutex = MONGO_MAKE_LATCH("KVDropPendingIdentReaper::_mutex");
// Drop-pending idents. Ordered by drop timestamp.
DropPendingIdents _dropPendingIdents;
};
} // namespace mongo
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