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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/logical_session_id.h"
#include "mongo/util/time_support.h"
namespace mongo {
class BSONObj;
class MigrationSessionId;
class OperationContext;
class Status;
class Timestamp;
class UUID;
namespace repl {
class OpTime;
} // namespace repl
/**
* This class is responsible for producing chunk documents to be moved from donor to a recipient
* shard and its methods represent cloning stages. Its lifetime is owned and controlled by a single
* migration source manager which registers it for notifications from the replication subsystem
* before calling startClone.
*
* Unless explicitly indicated, the methods on this class are not thread-safe.
*
* The pattern of using this interface is such that one thread instantiates it and registers it so
* it begins receiving notifications from the replication subsystem through the
* on[insert/update/delete]Op methods. It is up to the creator to decide how these methods end up
* being called, but currently this is done through the CollectionShardingState. The creator then
* kicks off the cloning as soon as possible by calling startClone.
*/
class MigrationChunkClonerSource {
MigrationChunkClonerSource(const MigrationChunkClonerSource&) = delete;
MigrationChunkClonerSource& operator=(const MigrationChunkClonerSource&) = delete;
public:
virtual ~MigrationChunkClonerSource();
/**
* Blocking method, which prepares the object for serving as a source for migrations and tells
* the recipient shard to start cloning. Before calling this method, this chunk cloner must be
* registered for notifications from the replication subsystem (not checked here).
*
* NOTE: Must be called without any locks and must succeed, before any other methods are called
* (except for cancelClone and [insert/update/delete]Op).
*/
virtual Status startClone(OperationContext* opCtx,
const UUID& migrationId,
const LogicalSessionId& lsid,
TxnNumber txnNumber) = 0;
/**
* Blocking method, which uses some custom selected logic for deciding whether it is appropriate
* for the donor shard to enter critical section.
*
* If it returns a successful status, the caller must as soon as possible stop writes (by
* entering critical section). On failure it may return any error. Known errors are:
* ExceededTimeLimit - if the maxTimeToWait was exceeded
*
* NOTE: Must be called without any locks.
*/
virtual Status awaitUntilCriticalSectionIsAppropriate(OperationContext* opCtx,
Milliseconds maxTimeToWait) = 0;
/**
* Tell the recipient shard to commit the documents it has cloned so far. Must be called only
* when it has been ensured that there will be no more changes happening to documents on the
* donor shard. If this is not observed, the recipient might miss changes and thus lose data.
*
* This must only be called once and no more methods on the cloner must be used afterwards
* regardless of whether it succeeds or not.
*
* Returns statistics about the move. These are informational only and should not be
* interpreted by the caller for any means other than reporting.
*
* NOTE: Must be called without any locks.
*/
virtual StatusWith<BSONObj> commitClone(OperationContext* opCtx, bool acquireCSOnRecipient) = 0;
/**
* Tells the recipient to abort the clone and cleanup any unused data. This method's
* implementation should be idempotent and never throw.
*
* NOTE: Must be called without any locks.
*/
virtual void cancelClone(OperationContext* opCtx) noexcept = 0;
// These methods are only meaningful for the legacy cloner and they are used as a way to keep a
// running list of changes, which need to be fetched.
/**
* Checks whether the specified document is within the bounds of the chunk, which this cloner
* is responsible for.
*
* NOTE: Must be called with at least IS lock held on the collection.
*/
virtual bool isDocumentInMigratingChunk(const BSONObj& doc) = 0;
/**
* Notifies this cloner that an insert happened to the collection, which it owns. It is up to
* the cloner's implementation to decide what to do with this information and it is valid for
* the implementation to ignore it.
*
* NOTE: Must be called with at least IX lock held on the collection.
*/
virtual void onInsertOp(OperationContext* opCtx,
const BSONObj& insertedDoc,
const repl::OpTime& opTime) = 0;
/**
* Notifies this cloner that an update happened to the collection, which it owns. It is up to
* the cloner's implementation to decide what to do with this information and it is valid for
* the implementation to ignore it.
*
* NOTE: Must be called with at least IX lock held on the collection.
*/
virtual void onUpdateOp(OperationContext* opCtx,
boost::optional<BSONObj> preImageDoc,
const BSONObj& postImageDoc,
const repl::OpTime& opTime,
const repl::OpTime& prePostImageOpTime) = 0;
/**
* Notifies this cloner that a delede happened to the collection, which it owns. It is up to the
* cloner's implementation to decide what to do with this information and it is valid for the
* implementation to ignore it.
*
* NOTE: Must be called with at least IX lock held on the collection.
*/
virtual void onDeleteOp(OperationContext* opCtx,
const BSONObj& deletedDocId,
const repl::OpTime& opTime,
const repl::OpTime& preImageOpTime) = 0;
/**
* Returns the migration session id associated with this cloner, so stale sessions can be
* disambiguated.
*/
virtual const MigrationSessionId& getSessionId() const = 0;
protected:
MigrationChunkClonerSource();
};
} // namespace mongo
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