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. 

}
        
        global_context->initializeKeeperDispatcher(can_initialize_keeper_async);
        FourLetterCommandFactory::registerCommands(*global_context->getKeeperDispatcher());
        auto config_getter = [this] () -> const Poco::Util::AbstractConfiguration &
        {
            return global_context->getConfigRef();
        };
        for (const auto & listen_host : listen_hosts)
        {
            
            const char * port_name = "keeper_server.tcp_port";
            createServer(
                config(), listen_host, port_name, listen_try,  false,
                servers_to_start_before_tables,
                [&](UInt16 port) -> ProtocolServerAdapter
                {
                    Poco::Net::ServerSocket socket;
                    auto address = socketBindListen(config(), socket, listen_host, port);
                    socket.setReceiveTimeout(config().getUInt64("keeper_server.socket_receive_timeout_sec", DBMS_DEFAULT_RECEIVE_TIMEOUT_SEC));
                    socket.setSendTimeout(config().getUInt64("keeper_server.socket_send_timeout_sec", DBMS_DEFAULT_SEND_TIMEOUT_SEC));
                    return ProtocolServerAdapter(
                        listen_host,
                        port_name,
                        "Keeper (tcp): " + address.toString(),
                        std::make_unique<TCPServer>(
                            new KeeperTCPHandlerFactory(
                                config_getter, global_context->getKeeperDispatcher(),
                                global_context->getSettingsRef().receive_timeout.totalSeconds(),
                                global_context->getSettingsRef().send_timeout.totalSeconds(),