Ordinary database engine is deprecated but there is no simple mean to change database engine to Atomic for existing databases.

Possible options:
- ALTER DATABASE MODIFY ENGINE query.
- Flag that triggers migration at ClickHouse startup.

The latter should be easier to implement. 

{
    auto backup = restorer.getBackup();
    if (!backup->hasFiles(data_path_in_backup))
        return;
    if (!num_data_files)
        return;
    if (!restorer.isNonEmptyTableAllowed() && total_bytes)
        RestorerFromBackup::throwTableIsNotEmpty(getStorageID());
    auto lock_timeout = getLockTimeout(restorer.getContext());
    restorer.addDataRestoreTask(
        [storage = std::static_pointer_cast<StorageLog>(shared_from_this()), backup, data_path_in_backup, lock_timeout]
        { storage->restoreDataImpl(backup, data_path_in_backup, lock_timeout); });
}
void StorageLog::restoreDataImpl(const BackupPtr & backup, const String & data_path_in_backup, std::chrono::seconds lock_timeout)
{
    WriteLock lock{rwlock, lock_timeout};
    if (!lock)
        throw Exception("Lock timeout exceeded", ErrorCodes::TIMEOUT_EXCEEDED);
    
    loadMarks(lock);
    
    saveFileSizes(lock);
    try
    {
        fs::path data_path_in_backup_fs = data_path_in_backup;
        
        for (const auto & data_file : data_files)