Question

So suppose 1 Gemfile uses devise 1.0 and another one also requires that same gem. Does bundle/rvm actually keeps 2 copies of the gem devise 1.0 when there are 2 different gemsets, one for each gemfile?

Answer 1

It depends from the gemset used. When you run bundle install it will compile a Gemfile.lock with the required gems and fix the gem at the highest version available at that time (unless you specify an exact version or a different version with ~> syntax).

Then when you add new gems to your Gemfile it still use that version unless you use the bundle update devise command. So as far as you not update manually devise it will use always the same gem.

Rvm will reuse the same gem if it’s compatible with the second Gemfile and you’re in the same gemset otherwise it will install a second copy of the devise gem.

To avoid that you can add shared gem in the @global gemset and they will be available to all your gemsets.

In every case it should not be an issue since a gem does not use a lot of disk space and different versions are handled using rvm/Gemfiles.