You can configure the client to be single-threaded. When you enable this option, the client doesn't use background threads to handle the client-server communication.
ClientConfiguration configuration = Db4oClientServer.newClientConfiguration();
configuration.networking().singleThreadedClient(true);
On some smaller embedded systems reducing the running threads improves the performance significantly.
Since all operations run in a single thread, the operations may take longer. Additionally you cannot receive messages and cannot use commit-callbacks on a single-threaded client.