Implicit vs explicit garbage collection

Question

Background:

I have created an API and I did profiling for memory usage & process time for each web service using this guide and memory profiler gem.

I created a table to keep all profiling results like this:

      Request      | Memory Usage(b) | Retained Memory(b) | Runtime(seconds)
----------------------------------------------------------------------------
  Post Login       | 444318          |   35649            | 1.254
  Post Register    | 232071          |   32673            | 0.611
  Get 10 Users     | 11947286        |   2670333          | 3.456
  Get User By ID   | 834953          |   131300           | 0.834

Note: all numbers are the average number of calling the same service 3 consecutive times.

And I read many guides and answers(like this and this) says that Garbage Collector is responsible for releasing memory and we should not explicitly interfere in memory management.

Then I just forced the Garbage Collector to start after each action (for test purpose) by adding the following filter in APIController:

after_action :dispose

def dispose
   GC.start
end

And I found that Memory usage is reduced too much (more than 70%), retained memory almost same before and runtime is reduced as well.

      Request      | Memory Usage(b) | Retained Memory(b) | Runtime(seconds)
----------------------------------------------------------------------------
  Post Login       | 38636           |   34628            | 1.023
  Post Register    | 37746           |   31522            | 0.583
  Get 10 Users     | 2673040         |   2669032          | 2.254
  Get User By ID   | 132281          |   128913           | 0.782

Questions:

Is it good practice to add such filter and what are the side effects?
I thought that runtime will be more than before, but it seems less, what can be the reason?

Update:

I'm using Ruby 2.3.0 and I've used gc_tracer gem to monitor heap status because I'm afraid to have old garbage collection issues highlighted in Ruby 2.0 & 2.1

The issue is that the Ruby GC is triggered on total number of objects, and not total amount of used memory

Then to do a stress test, I run the following:

while true
  "a" * (1024 ** 2)
end

and result is that memory usage does not exceed the following limits (it was exceeding before and GC wont be triggered):

RUBY_GC_MALLOC_LIMIT_MAX
RUBY_GC_OLDMALLOC_LIMIT_MAX

So now I'm pretty sure that same GC issues of 2.0 & 2.1 don't exist anymore in 2.3, but still getting the following positive results by adding above mentioned filter (after_action :dispose):

Heap memory enhanced by 5% to 10% (check this related question)
General execution time enhanced by 20% to 40% (test done using third party tool Postman which consumes my API)

I'm still looking for answers to my two questions above.

Any feedback would be greatly appreciated

Implicit vs explicit garbage collection

0 Answers0