Maybe this will help someone, as well...we've been trying to collect all of the different tuning and implementation information on the Ruby GC in one place:
https://www.omniref.com/ruby/2.1.2/symbols/GC#annotation=88&...
Re:Incremental GC in Ruby MRI
by jerhinesmith on Friday August 15, 2014 @04:17PM
(#8183934)
That's actually a huge help. What I've also been looking for (and haven't been able to find) is a good guide on How to Tune your GC settings. Aman Gupta has gotten the closest so far* (I think), but I'd really love a step-by-step of "OK, open your console, run `GC.start`, take note of this property because it means X and indicates that Y would be a good setting for Z, etc. etc"
It would be interesting or useful to know more about it, but what I think is that ideally a right impementation of a GC should not require any tweeks from the outside... and I am pretty sure you are not going to get any signifcant performance boost by using different GC values than default.
I've been collecting bookmarks on how to properly tune the GC environment variables in these situations -- hopefully they'll help someone else:
Heroku discussion: https://discussion.heroku.com/t/tuning-rgengc-2-1-on-heroku/...
Using Out-of-band GC on 2.1: http://tmm1.net/ruby21-oobgc/