Garbage collector tuning in Ruby 2.0

Question

I was wondering if the GC tuning used for ruby 1.9.x is still relevant in 2.0 with the new implementation of the GC. If so, are there any new things that we can configure on the new version?

I am talking about the following setups

RUBY_HEAP_MIN_SLOTS=600000  RUBY_GC_MALLOC_LIMIT=59000000 RUBY_HEAP_FREE_MIN=100000 

Answer 1

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)