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. 

#else
            UNUSED(port);
            throw Exception{"SSL support for TCP protocol is disabled because Poco library was built without NetSSL support.",
                            ErrorCodes::SUPPORT_IS_DISABLED};
#endif
        });
        port_name = "mysql_port";
        createServer(config, listen_host, port_name, listen_try, start_servers, servers, [&](UInt16 port) -> ProtocolServerAdapter
        {
            Poco::Net::ServerSocket socket;
            auto address = socketBindListen(config, socket, listen_host, port,  true);
            socket.setReceiveTimeout(Poco::Timespan());
            socket.setSendTimeout(settings.send_timeout);
            return ProtocolServerAdapter(
                listen_host,
                port_name,
                "MySQL compatibility protocol: " + address.toString(),
                std::make_unique<TCPServer>(new MySQLHandlerFactory(*this), server_pool, socket, new Poco::Net::TCPServerParams));
        });
        port_name = "postgresql_port";
        createServer(config, listen_host, port_name, listen_try, start_servers, servers, [&](UInt16 port) -> ProtocolServerAdapter
        {
            Poco::Net::ServerSocket socket;
            auto address = socketBindListen(config, socket, listen_host, port,  true);
            socket.setReceiveTimeout(Poco::Timespan());
            socket.setSendTimeout(settings.send_timeout);
            return ProtocolServerAdapter(
                listen_host,
                port_name,
                "PostgreSQL compatibility protocol: " + address.toString(),