Ruby Garbage Collect

Garbage collect in ruby?

No, there is no way to do it in Ruby.

There is a method called GC::start, and the documentation even says:

Initiates garbage collection, even if manually disabled.

But that is not true. GC::start is simply an advisory from your code to the runtime that it would be safe for your application to run a garbage collection now. But that is only a suggestion. The runtime is free to ignore this suggestion.

The majority of programming languages with automatic memory management do not give the programmer control over the garbage collector.

If Ruby had a method to force a garbage collection, then it would be impossible to implement Ruby on the JVM and neither JRuby nor TruffleRuby could exist, it would be impossible to implement Ruby on .NET and IronRuby couldn't exist, it would be impossible to implement Ruby on ECMAScript and Opal couldn't exist, it would be impossible to implement Ruby using existing high-performance garbage collectors and RubyOMR couldn't exist.

Since it is in generally desirable to give implementors freedom to implement optimizations and make the language faster, languages are very cautious on specifying features that so drastically restrict what an implementor can do.

I am quite surprised that R has such a feature, especially since that means it is impossible to implement high-performance implementations like FastR in a way that is compliant with the language specification. FastR is up to more than 35× faster than GNU R, so it is obvious why it is desirable for something like FastR to exist. But one of the ways FastR is faster, is that it uses a third-party high-performance garbage collected runtime (either the GraalVM or the JVM) that does not allow control over garbage collection, and thus FastR can never be a compliant R implementation.

Interestingly, the documentation of gc() has this to say:

[T]he primary purpose of calling gc is for the report on memory usage.

Ruby garbage collect

There are occasions when it's necessary to kick it off, but usually it works fine by itself. I've had situations where an app will chew through 1GB of memory if left unchecked, pushing deep into swap, where triggering GC.start intermittently will cut that to 100MB.

The trouble is that calling this method is very expensive and can slow down your application considerably if used aggressively.

Garbage collector in Ruby on Rails?

Rails is a framework, not a language. The language behind Rails is called Ruby.

This means there is no notion of Garbage Collector in Rails. You should search for documentation about the Ruby Garbage Collector.

You can start from the Ruby GC module. The GC module provides an interface to Ruby’s mark and sweep garbage collection mechanism.

Depending on the Ruby language version, the Garbage Collector may have a different behavior. The article How Ruby Manages Memory and Garbage Collection describes the Ruby 1.9 Garbage Collector. In Ruby 2.0 the GC has been improved and the implementation changed a bit.

Garbage Collection in Ruby 2.x

No, these 100s of keys will increase heap_length over the time and when you reassign this reference variable to nil object the GC will not be called. Even if you call GC.start at this point the heap_free_num value will be an increase but total heap_length will remain the same. when you assign a reference variable nil. It will not call the Garbage Collector because the GC is only called in case ruby process needed to increase the heap_length by the introduction of a new variable or in a case of a new piece of code being call.

Why isn't this simple class garbage collected in Ruby console?

It seems this was already answered in another question

Pry stores the output of the last 100 commands and thus the object can't actually be garbage collected.