Create a new database by restoring from a completed backup. The new database must be in the same project and in an instance with the same instance configuration as the instance containing the backup. The returned database long-running operation has a name of the format projects//instances//databases//operations/, and can be used to track the progress of the operation, and to cancel it. The metadata field type is RestoreDatabaseMetadata. The response type is Database, if successful. Cancelling the returned operation will stop the restore and delete the database. There can be only one database being restored into an instance at a time. Once the restore operation completes, a new restore operation can be initiated, without waiting for the optimize operation associated with the first restore to complete.