Why is Ray Tune only using one worker?

Question

Ray is starting only one worker, even though enough GPUs and CPUs are available to launch more workers. How can I increase the number of workers?

Answer 1

You need to set the number of samples ray should collect, otherwise ray collects only a single sample and therefore only launches a single worker. The following would enable multiple workers:

tune.run(
        main, 
        resources_per_trial=resources,
        num_samples=1000
        )