I have investigated this in detail and the reason for this is really ridiciulous - 80% of this time is spend on executing "require" statements and this is due to really bad design of RubyGems and/or Bundler. They both do their job by augmenting $LOAD_PATH to include all directories containing gem contents. If you then look into how Ruby deals with the $LOAD_PATH, it turns out each time you do a "require" it will go through all of those directories and their subdirectories in search for a file matching what you have required. I used strace to see how this impacts doing "rails console" on an application with around 30 gems - it ended up doing 35000 open calls that ended up with ENOENT. It is beyond my mind how this can remain unfixed for so long. If RubyGems instead maintained a cache from all the gem directories, it could map requires to files without touching the filesystem and it would work many times as fast. Even creating a cache at runtime and then using it for the lookup would be many times as fast. Unfortunately, it is hard to determine a strategy for building this cache that would map the requires to files in exactly the same was as RubyGems, because RubyGems has some pretty weird strategy for determining which files take priority over which files when you do an ambiguous require. Because of this, I haven't yet succeeded in implementing a fix myself and I'm not 100% sure if it is possible. I also tried to contact one of the Bundler guys, but so far haven't had any reply about this.