There’s a fair bit of confusion about these GC tuning parameters. REE (which is a fork of Ruby 1.8.7) introduced its own parameters first, and later Ruby (starting in 1.9.2) introduced its own (similar) parameters. Ruby 1.9.3 made them customizable via environment variables, and Ruby 2.1.0 added a lot more.
This blog post goes into great detail about garbage collection in MRI and what all the tuning variables mean.
Here’s a complete list of all the tuning variables for each Ruby version:
REE source
- RUBY_HEAP_MIN_SLOTS
- RUBY_HEAP_SLOTS_INCREMENT
- RUBY_HEAP_SLOTS_GROWTH_FACTOR
- RUBY_GC_MALLOC_LIMIT
- RUBY_HEAP_FREE_MIN
Ruby 1.9.2 source source
(Hard-coded, but customizable via environment variables with this patch)
- GC_MALLOC_LIMIT
- HEAP_MIN_SLOTS
- FREE_MIN
Ruby 1.9.3 source
- RUBY_GC_MALLOC_LIMIT
- RUBY_HEAP_MIN_SLOTS
- RUBY_FREE_MIN
Ruby 2.0.0 source
Same as Ruby 1.9.3
Ruby 2.1.0 source
- RUBY_GC_HEAP_INIT_SLOTS (obsoletes RUBY_HEAP_MIN_SLOTS)
- RUBY_GC_HEAP_FREE_SLOTS (obsoletes RUBY_FREE_MIN)
- RUBY_GC_HEAP_GROWTH_FACTOR (new)
- RUBY_GC_HEAP_GROWTH_MAX_SLOTS (new)
- RUBY_GC_MALLOC_LIMIT
- RUBY_GC_MALLOC_LIMIT_MAX (new)
- RUBY_GC_MALLOC_LIMIT_GROWTH_FACTOR (new)
- RUBY_GC_OLDMALLOC_LIMIT (new)
- RUBY_GC_OLDMALLOC_LIMIT_MAX (new)
- RUBY_GC_OLDMALLOC_LIMIT_GROWTH_FACTOR (new)
Ruby 2.1.1 source
- RUBY_GC_HEAP_OLDOBJECT_LIMIT_FACTOR (new)