Just a hack to make it easier to understand GC.stat in Ruby 2.0 and 2.1 (made for a tech talk)

human_gc_stats.rb

# This is an attempt to translate GC.stat to a more understandable format for humans
# from @samsaffron
# http://samsaffron.com/archive/2013/11/22/demystifying-the-ruby-gc?utm_source=rubyweekly&utm_medium=email
# http://samsaffron.com/archive/2014/04/08/ruby-2-1-garbage-collection-ready-for-production
def gc_stats
  stats = GC.stat
  space_count = ObjectSpace.count_objects

  objects_per_heap = space_count[:TOTAL] / stats[:heap_used]
  report = {
                                        objects_per_heap: objects_per_heap,
                                   heaps_with_used_slots: stats[:heap_used],
                                   total_heaps_allocated: stats[:heap_length],
                             total_heaps_allocated_in_mb: (stats[:heap_length] * (2 << 13)).to_f / (2 << 19),
                               heaps_to_allocate_next_gc: stats[:heap_increment],
                                            live_objects: stats[:heap_live_num] || stats[:heap_live_slot],
                        allocated_minus_freed_since_boot: stats[:total_allocated_object] - stats[:total_freed_object],
                      total_objects_allocated_since_boot: stats[:total_allocated_object],
                          total_objects_freed_since_boot: stats[:total_freed_object],
                                           total_gc_runs: stats[:count],
  }
  if RUBY_VERSION !~ /^2\.1/
    report.merge!(
                            'RUBY_GC_MALLOC_LIMIT in mb' => (stats[:malloc_limit] ? stats[:malloc_limit].to_f : (ENV['RUBY_GC_MALLOC_LIMIT'] || 8000000).to_f) / (2 << 19),
                                   'RUBY_HEAP_MIN_SLOTS' => (ENV['RUBY_HEAP_MIN_SLOTS'] || 10000).to_i,
                                         'RUBY_FREE_MIN' => (ENV['RUBY_FREE_MIN'] || 4096).to_i,
                               magic_set_heaps_increment: "heaps_used * 1.8",
                      magic_before_gc_sweep_do_heap_free: "(heaps_used * HEAP_OBJ_LIMIT) * 0.65",
                          magic_before_gc_sweep_free_min: "(heaps_used * HEAP_OBJ_LIMIT) * 0.2",
    )
  else
    report.merge!(
                                          major_gc_count: stats[:major_gc_count],
                                          minor_gc_count: stats[:minor_gc_count],
                                 remembered_shady_object: stats[:remembered_shady_object],
                           remembered_shady_object_limit: stats[:remembered_shady_object_limit],
                          total_heaps_allocated_for_eden: stats[:heap_eden_page_length],
                          total_heaps_allocated_for_tomb: stats[:heap_tomb_page_length],
      'RUBY_GC_HEAP_INIT_SLOTS (ex RUBY_HEAP_MIN_SLOTS)' => (ENV['RUBY_GC_HEAP_INIT_SLOTS'] || 10000).to_i,
            'RUBY_GC_HEAP_FREE_SLOTS (ex RUBY_FREE_MIN)' => (ENV['RUBY_GC_HEAP_FREE_SLOTS'] || 4096).to_i,
                            'RUBY_GC_HEAP_GROWTH_FACTOR' => (ENV['RUBY_GC_HEAP_GROWTH_FACTOR'] || 1.8),
                         'RUBY_GC_HEAP_GROWTH_MAX_SLOTS' => (ENV['RUBY_GC_HEAP_GROWTH_MAX_SLOTS'] || 0),
                   'RUBY_GC_HEAP_OLDOBJECT_LIMIT_FACTOR' => (ENV['RUBY_GC_HEAP_OLDOBJECT_LIMIT_FACTOR'] || 2.0),
                            'RUBY_GC_MALLOC_LIMIT in mb' => (ENV['RUBY_GC_MALLOC_LIMIT'] || 16777216).to_f / (2 << 19),
                        'RUBY_GC_MALLOC_LIMIT_MAX in mb' => (ENV['RUBY_GC_MALLOC_LIMIT_MAX'] || 33554432).to_f / (2 << 19), 
                    'RUBY_GC_MALLOC_LIMIT_GROWTH_FACTOR' => (ENV['RUBY_GC_MALLOC_LIMIT_GROWTH_FACTOR'] || 1.4),
                                            malloc_limit: stats[:malloc_limit].to_f / (2 << 19),
                     malloc_increase_since_last_minor_gc: stats[:malloc_increase].to_f / (2 << 19),
                         'RUBY_GC_OLDMALLOC_LIMIT in mb' => (ENV['RUBY_GC_OLDMALLOC_LIMIT'] || 16777216).to_f / (2 << 19),
                        'RUBY_GC_MALLOC_LIMIT_MAX in mb' => (ENV['RUBY_GC_MALLOC_LIMIT_MAX'] || 134217728).to_f / (2 << 19), 
                    'RUBY_GC_MALLOC_LIMIT_GROWTH_FACTOR' => (ENV['RUBY_GC_MALLOC_LIMIT_GROWTH_FACTOR'] || 1.2),
                                         oldmalloc_limit: stats[:oldmalloc_limit].to_f / (2 << 19),
                     malloc_increase_since_last_major_gc: stats[:oldmalloc_increase].to_f / (2 << 19)
    )
  end
  report
end