allocated memory issue

[netwire88]

I have the following in my Gemfile

ruby '2.7.5'
gem 'rails', '~> 6.1', '>= 6.1.4'
group :development do
  gem 'derailed_benchmarks', '~> 2.1', '>= 2.1.1'
end

However, when I run bundle exec derailed bundle:objects production, I see the following

allocated memory by gem
-----------------------------------
  43060426  dead_end-1.1.7

and when I run bundle exec gem dep -R
I see that dead_end is only used by derailed_benchmarks

Gem dead_end-3.1.0
  Used by
    derailed_benchmarks-2.1.1 (dead_end (>= 0))

I'm a bit confused why:

1. the gem's showing up in production
2. it seems to be creating huge memory footprint upon launching of app

Any thoughts?

I'm not sure if it's related to this issue action_mailbox/engine still loads even after not requiring it in application.rb where @andrehjr says it's derailed_benchmark's use of require "action_controller/railtie"

[schneems]

the gem's showing up in production

Because it's added to derailed in development. So when you're running in production for real (not just simulating it with derailed) you also won't have dead_end.

it seems to be creating huge memory footprint upon launching of app

I've described the issue here ruby/syntax_suggest#124 (comment). The TLDR is that any gem that patches into require (such as dead_end or bootsnap etc) will show up here as derailed ALSO patches into require and that's how it gets it's info.

If it's causing confusion we could perhaps introduce an env var into dead_end that would optionally disable the monekypatching behavior. We could also move it from a general derailed require to a per-task require.

[schneems]

Also that output is from memory_profiler. One question to ask is: why isn't this a problem for bootsnap? Did get it special cased somehow?

[beporter]

Just ran into this myself, and was admittedly confused when the single largest consumer of "allocated memory by gem" by a long way was (indirectly) from the package I just installed to examine the memory itself (derailed_benchmark).

$ bundle exec derailed bundle:objects
Measuring objects created by gems in groups [:default, "production"]
Total allocated: 94891342 bytes (956756 objects)
Total retained:  19576854 bytes (177325 objects)

allocated memory by gem
-----------------------------------
  60670886  dead_end-3.1.1
   6590809  mime-types-3.3.1
   4019827  json-2.5.1
   3301861  set

# **SNIP**

Thankfully this GitHub issue came up relatively quick from searching, but it's not a particularly great first-time experience to immediately get led on a (short) wild goose chase inflicted by this very gem. If there is a way to suppress derailed's own dependencies from the output (when they are not otherwise used by the host application of course), I think I'm in favor of that.