Why Do Heroku Stack Traces indicate Ruby 1.9.1 is in use?

Question

Recently saw this stack trace on our Heroku app on cedar

/usr/local/lib/ruby/1.9.1/uri/common.rb:156:in `split'
/usr/local/lib/ruby/1.9.1/uri/common.rb:174:in `parse'
/usr/local/lib/ruby/1.9.1/uri/common.rb:628:in `parse'

Why is it using Ruby 1.9.1?

My Gemfile is not specifying a Ruby version. Heroku's docs suggest that we should be getting the Cedar default of 1.9.2

https://devcenter.heroku.com/articles/ruby-versions

EDIT:

ruby -v appears to report the correct version

$ heroku run "ruby -v"
Running `ruby -v` attached to terminal... up, run.2594
ruby 1.9.2p290 (2011-07-09 revision 32553) [x86_64-linux]

what does `ruby --version` report it will use whatever version you have, generally the `which ruby` version depending on how you start it. — Grady Player, Mar 08 '13 at 15:05
well irb and ruby are different executables. do you have multiple versions in your path... `whereis ruby` — Grady Player, Mar 08 '13 at 15:16

score 4 · Accepted Answer · edited Jun 20 '20 at 09:12

It's not actually using Ruby 1.9.1 -- as this answer from Marc-André Lafortune explains, it has to do with the C interface, which hasn't changed since Ruby 1.9.1.

In Ruby 1.9.0, the C interface was changed from the Ruby 1.8 series.

Gems that compile to native code had to be recompiled.

The interface was again changed in Ruby 1.9.1 and kept the same in Ruby 1.9.2 & 3. This explains the 1.9.1 you are seeing in your path.

The idea is that you can install different versions of Ruby on your system and that gems would be shared within groups having the same C api. So Ruby 1.8.6 and 1.8.7 could share their gems, and so could Ruby 1.9.1, .2 and .3.

It's not necessarily the best idea, though. In any case, most people use rvm to access different versions of Ruby and rvm keeps gems separate for each version, irrespective of the C api version.

Why Do Heroku Stack Traces indicate Ruby 1.9.1 is in use?

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