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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/bson/bsonobj.h"
#include "mongo/db/s/database_sharding_state.h"
#include "mongo/s/request_types/move_primary_gen.h"
#include "mongo/s/shard_id.h"
#include "mongo/util/timer.h"
namespace mongo {
class OperationContext;
class Shard;
struct ShardingStatistics;
class Status;
/**
* The donor-side movePrimary state machine. This object must be created and owned by a single
* thread, which controls its lifetime and should not be passed across threads. Unless explicitly
* indicated its methods must not be called from more than one thread and must not be called while
* any locks are held.
*
* The intended workflow is as follows:
* - Acquire a distributed lock on the database whose primary is about to be moved.
* - Instantiate a MovePrimarySourceManager on the stack.
* - Call clone to start and finish cloning of the unsharded collections.
* - Call enterCriticalSection to cause the shard to enter in 'read only' mode while the config
* server is notified of the new primary.
* - Call commitOnConfig to indicate the new primary in the config server metadata.
* - Call cleanStaleData to drop now-unused collections (and potentially databases) on the
* old primary.
*
* At any point in time it is safe to let the MovePrimarySourceManager object go out of scope in
* which case the destructor will take care of clean up based on how far we have advanced.
*/
class MovePrimarySourceManager {
MovePrimarySourceManager(const MovePrimarySourceManager&) = delete;
MovePrimarySourceManager& operator=(const MovePrimarySourceManager&) = delete;
public:
/**
* Instantiates a new movePrimary source manager. Must be called with the distributed lock
* acquired in advance (not asserted).
*
* May throw any exception. Known exceptions (TODO) are:
* - InvalidOptions if the operation context is missing database version
* - StaleConfigException if the expected database version does not match what we find it
* to be after acquiring the distributed lock.
*/
MovePrimarySourceManager(OperationContext* opCtx,
ShardMovePrimary requestArgs,
StringData dbname,
ShardId& fromShard,
ShardId& toShard);
~MovePrimarySourceManager();
/**
* Returns the namespace for which this source manager is active.
*/
NamespaceString getNss() const;
/**
* Contacts the recipient shard and tells it to start cloning the specified chunk. This method
* will fail if for any reason the recipient shard fails to complete the cloning sequence.
*
* Expected state: kCreated
* Resulting state: kCloning on success, kDone on failure
*/
Status clone(OperationContext* opCtx);
/**
* Once this call returns successfully, no writes will be happening on this shard until the
* movePrimary is committed. Therefore, commitMovePrimaryMetadata must be called as soon as
* possible afterwards.
*
* Expected state: kCloneCaughtUp
* Resulting state: kCriticalSection on success, kDone on failure
*/
Status enterCriticalSection(OperationContext* opCtx);
/**
* Persists the updated DatabaseVersion on the config server and leaves the critical section.
*
* Expected state: kCriticalSection
* Resulting state: kNeedCleanStaleData
*/
Status commitOnConfig(OperationContext* opCtx);
/**
* Clears stale collections (and potentially databases) on the old primary.
*
* Expected state: kNeedCleanStaleData
* Resulting state: kDone
*/
Status cleanStaleData(OperationContext* opCtx);
/**
* May be called at any time. Unregisters the movePrimary source manager from the database and
* logs an error in the change log to indicate that the migration has failed.
*
* Expected state: Any
* Resulting state: kDone
*/
void cleanupOnError(OperationContext* opCtx);
private:
static BSONObj _buildMoveLogEntry(const std::string& db,
const std::string& from,
const std::string& to) {
BSONObjBuilder details;
details.append("database", db);
details.append("from", from);
details.append("to", to);
return details.obj();
}
/**
* Updates CSRS metadata in config.databases collection to move the given primary database on
* its new shard.
*/
Status _commitOnConfig(OperationContext* opCtx);
// Used to track the current state of the source manager. See the methods above, which have
// comments explaining the various state transitions.
enum State {
kCreated,
kCloning,
kCloneCaughtUp,
kCriticalSection,
kCloneCompleted,
kNeedCleanStaleData,
kDone
};
/**
* Called when any of the states fails. May only be called once and will put the migration
* manager into the kDone state.
*/
void _cleanup(OperationContext* opCtx);
// The parameters to the movePrimary command
const ShardMovePrimary _requestArgs;
// The database whose primary we are moving.
const StringData _dbname;
// The donor shard
const ShardId& _fromShard;
// The recipient shard
const ShardId& _toShard;
// Collections that were cloned to the new primary
std::vector<NamespaceString> _clonedColls;
// Indicates whether sharded collections exist on the old primary.
bool _shardedCollectionsExistOnDb;
// Times the entire movePrimary operation
const Timer _entireOpTimer;
// The current state. Used only for diagnostics and validation.
State _state{kCreated};
// Information about the movePrimary to be used in the critical section.
const BSONObj _critSecReason;
};
} // namespace mongo
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