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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/base/status_with.h"
#include "mongo/db/s/balancer/balancer_policy.h"
#include "mongo/s/request_types/migration_secondary_throttle_options.h"
namespace mongo {
/**
* RAII class that handles writes to the config.migrations collection for a migration that comes
* through the balancer.
*
* A migration must have an entry in the config.migrations collection so that the Balancer can
* recover from stepdown/crash. This entry must be entered before a migration begins and then
* removed once the migration has finished.
*
* This class should only be used by the Balancer!
*/
class ScopedMigrationRequest {
MONGO_DISALLOW_COPYING(ScopedMigrationRequest);
public:
/**
* Deletes this migration's entry in the config.migrations collection, using majority write
* concern. If there is a balancer stepdown/crash before the write propagates to a majority of
* servers, that is alright because the balancer recovery process will handle it.
*
* If keepDocumentOnDestruct() has been called, then no attempt to remove the document is made.
*/
~ScopedMigrationRequest();
ScopedMigrationRequest(ScopedMigrationRequest&& other);
ScopedMigrationRequest& operator=(ScopedMigrationRequest&& other);
/**
* Inserts an unique migration entry in the config.migrations collection. If the write is
* successful, a ScopedMigrationRequest object is returned; otherwise, the write error.
*
* The destructor will handle removing the document when it is no longer needed.
*/
static StatusWith<ScopedMigrationRequest> writeMigration(OperationContext* opCtx,
const MigrateInfo& migrate,
bool waitForDelete);
/**
* Creates a ScopedMigrationRequest object without inserting a document into config.migrations.
* The destructor will handle removing the migration document when it is no longer needed.
*
* This should only be used on Balancer recovery when a config.migrations document already
* exists for the migration.
*/
static ScopedMigrationRequest createForRecovery(OperationContext* opCtx,
const NamespaceString& nss,
const BSONObj& minKey);
/**
* Do not call if keepDocumentOnDestruct has been called previously: it will invariant.
*
* Attempts to delete this migration's entry in the config.migrations collection using majority
* write concern. If successful, clears the operation context so that the destructor will not
* redundantly try to remove an already successfully deleted document.
*/
Status tryToRemoveMigration();
/**
* Do not call if tryToRemoveMigration has been called previously: it may invariant.
*
* Clears the operation context so that the destructor will not remove the config.migrations
* document for the migration.
*
* This should only be used on the Balancer when it is interrupted and must leave entries in
* config.migrations so that ongoing migrations can be recovered later.
*/
void keepDocumentOnDestruct();
private:
ScopedMigrationRequest(OperationContext* opCtx,
const NamespaceString& nss,
const BSONObj& minKey);
// Need an operation context with which to do a write in the destructor.
OperationContext* _opCtx;
// ns and minkey are needed to identify the migration document when it is removed from
// config.migrations by the destructor.
NamespaceString _nss;
BSONObj _minKey;
};
} // namespace mongo
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