Backtraces are very useful tools when debugging problems in Ruby programs. Unfortunately, backtrace generation is expensive for deep callstacks. In older versions of Ruby, this is true even if you only want a partial backtrace, such as a single backtrace frame. Thankfully, Ruby 3 has been optimized so that it no longer processes unnecessary backtrace frames, which can greatly speed up the generation of partial backtraces. Join me for an interesting look a Ruby backtraces, how they are generated, how we optimized partial backtraces in Ruby 3, and how we fixed bugs in the optimization in 3.0.1.