mlr3 properly setting up parallelization

Question

Say I have a machine with 32 cores and want to execute a nested CV of 5 outer folds and 3 inner folds as efficiently as possible.

On the outer fold, I benchmark two or more learners, on the inner fold I tune hyperparams for one or n-k of the learners.

How to set batch_size and future::plan()?

How does term_eval depend on the batch size?

Would this be sensible? My hunch would be to better run the inner loop in parallel. But I am unsure about term_evals and batch_size.

lrn1 <- auto_tuner(
  method = "random_search",
  learner = lrn1,
  resampling = rsmp("cv", folds = 3),
  measure = msr("classif.auc"),
  term_evals = 100,
  batch_size = 10,
  store_models = TRUE
)

design = benchmark_grid(task = task, learner = c(lrn1, lrn2), resampling = rsmp("cv", folds = 5))

# Runs the inner loop in parallel and the outer loop sequentially
future::plan(list("sequential", "multisession"))

bmr = benchmark(design, store_models = TRUE)

score 5 · Accepted Answer · answered Nov 28 '22 at 13:18

If you use rsmp("cv", folds = 3) and set batch_size = 10, 30 cores are used at once (3 folds x 10 configurations).

How does term_eval depend on the batch size?

term_eval does not depend on batch_size. batch_size specifies how many configurations are evaluated until the terminator is checked. In your example, the terminator is checked after 10 configurations. But you still have 90 configurations left, so the tuning continues. The terminator checks again after 10 configurations and so on. When 100 configurations are evaluated the terminator stops the tuning. The batch_size also determines how many configurations are evaluated in parallel.

My hunch would be to better run the inner loop in parallel.

Yes, run the inner loop in parallel i.e. keep future::plan(list("sequential", "multisession")).

mlr3 properly setting up parallelization

1 Answers1