RUBY_HEAP_MIN_SLOTS (default 10_000) - The initial number of heap slots and the minimum number of slots at any time. One slot for a heap can contain one Ruby object.
RUBY_HEAP_FREE_MIN (default 4_096) - the number of free slots that should be present after the garbage collector has completed assembly. If there are fewer than indicated, he allocates new ones in accordance with the parameters RUBY_HEAP_SLOTS_INCREMENT and RUBY_HEAP_SLOTS_GROWTH_FACTOR
RUBY_HEAP_SLOTS_INCREMENT ( 10_000 by default) - the number of new slots for distribution when all initial slots are used. Second pile.
RUBY_HEAP_SLOTS_GROWTH_FACTOR (default 1.8) - multiplication factor used to determine the number of new slots for distribution (RUBY_HEAP_SLOTS_INCREMENT * multiplication factor). For heaps No. 3 and further.
RUBY_GC_MALLOC_LIMIT (default is 8_000_000) - the number of C data structures that can be allocated before the garbage collector starts.
The default settings for the Ruby garbage collector are not optimized for Rails, which uses a lot of memory and often creates and destroys huge objects. The optimal values depend on the application itself, and you can profile garbage collection in different settings: http://www.ruby-doc.org/core-2.0/GC/Profiler.html
You can also control the GC using New Relic, gdb.rb or using gems such as scrap ( https://github.com/cheald/scrap/tree/master ).
Here are some articles you might be interested in:
https://www.coffeepowered.net/2009/06/13/fine-tuning-your-garbage-collector/ http://technology.customink.com/blog/2012/03/16/simple-garbage-collection- tuning-for-rails / http://snaprails.tumblr.com/post/241746095/rubys-gc-configuration