[ruby-core:93550] [Ruby master Bug#11448] Requiring a given library may take 23x longer depending on `require` context

Issue #11448 has been updated by jeremyevans0 (Jeremy Evans).

Status changed from Open to Closed

I don't think this is a significant issue with current Ruby, though it was certainly a bigger issue in previous versions.  From some testing:

```
$ ruby22 -r active_record -e "t = Time.now; require 'English'; p(Time.now - t)" 
0.004071895
$ ruby22 -e "t = Time.now; require 'English'; p(Time.now - t)" 
0.000901009

$ ruby27 -r active_record -e "t = Time.now; require 'English'; p(Time.now - t)" 
0.00102763
$ ruby27 -e "t = Time.now; require 'English'; p(Time.now - t)"                  
0.000822299
```

So on my system, it was about a 4.5x difference in 2.2, but is only about a 25% difference in 2.7.  There will always be at least a small difference due to the fact that Ruby needs to do a linear search of the load path, and requiring the `active_record` library in this case almost doubles the size of the load path.  So I think this can be closed.

----------------------------------------
Bug #11448: Requiring a given library may take 23x longer depending on `require` context
https://bugs.ruby-lang.org/issues/11448#change-79117

* Author: rafBM (Rafa謖 Blais Masson)
* Status: Closed
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.2.2p95 (2015-04-13 revision 50295) [x86_64-darwin14]
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN
----------------------------------------
I was trying to narrow down the longest things to require during Rails boot when I stumbled on this.

Add two lines in `securerandom.rb` in order to output the time taken to `require 'openssl'`:

~~~
 # -*- coding: us-ascii -*-
 begin
+  start = Time.now
   require 'openssl'
+  puts Time.now - start
 rescue LoadError
 end

 # == Secure random number generator interface.
 # ...
~~~

Now run a script containing just this:

~~~
require 'securerandom'
~~~

Average output: `0.038829`

But run a similar script that requires a higher-level library, like:

~~~
require 'action_mailer'
~~~

Average output: `0.907959`

This still measures the time taken to `require 'openssl'` only. Why is it 23x times slower? Because it is nested within other `require` calls? When requiring `action_mailer`, this is the tree of files required to get to `securerandom`:

~~~
require 'action_mailer'
  require 'abstract_controller'
    require 'active_support/rails'
      require 'active_support/deprecation'
        require 'active_support/deprecation/behaviors'
          require 'active_support/notifications'
            require 'active_support/notifications/instrumenter'
              require 'securerandom'
~~~

When starting one level down, time to `require 'openssl'` is cut in half:

~~~
require 'abstract_controller'
~~~

Average output: `0.465274`



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