How can I know the best GC settings for my Ruby app?

The Ruby garbage collector has been flagged as the crux of Ruby performance and memory use for a long time. It has improved a lot over the last years, but there's still a lot to tune and control. The default configuration is not suitable and optimal for most applications, and neither is there a one-size-fits-all set of tuned parameters that would suit every app. However, hand-tuning the GC parameters is a slippery slope to navigate for most developers.