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. 

}
                metadata.total_dictionaries += create_query->is_dictionary;
            }
        }
        catch (Exception & e)
        {
            e.addMessage("Cannot parse definition from metadata file " + full_path.string());
            throw;
        }
    };
    iterateMetadataFiles(local_context, process_metadata);
    size_t objects_in_database = metadata.parsed_tables.size() - prev_tables_count;
    size_t dictionaries_in_database = metadata.total_dictionaries - prev_total_dictionaries;
    size_t tables_in_database = objects_in_database - dictionaries_in_database;
    LOG_INFO(log, "Metadata processed, database {} has {} tables and {} dictionaries in total.",
             TSA_SUPPRESS_WARNING_FOR_READ(database_name), tables_in_database, dictionaries_in_database);
}
void DatabaseOrdinary::loadTableFromMetadata(ContextMutablePtr local_context, const String & file_path, const QualifiedTableName & name, const ASTPtr & ast,
    LoadingStrictnessLevel mode)
{
    assert(name.database == TSA_SUPPRESS_WARNING_FOR_READ(database_name));
    const auto & create_query = ast->as<const ASTCreateQuery &>();
    tryAttachTable(
        local_context,
        create_query,
        *this,
        name.database,
        file_path, LoadingStrictnessLevel::FORCE_RESTORE <= mode);
}
void DatabaseOrdinary::startupTables(ThreadPool & thread_pool, LoadingStrictnessLevel )