XRay provides a lightweight yet powerful toolbox for troubleshooting Ruby applications when things stop making sense. Includes GDB and DTrace tooling.

*** GDB ***

Copy +gdb_macros+ file provided in the gem as your ~/.gdbinit file.

*** Fire DTrace Application Probes ***

See XRay::DTrace::Tracer

*** Out-of-the-box Rails DTrace Instrumentation ***

You are one require away from triggering automatically DTrace events for 
Rails requests, database access and template rendering. As simple as 

   # environment.rb
   Rails::Initializer.run do |config|

     ...

     config.after_initialize do
       require "xray/dtrace/rails/enable_tracing"
     end  
   end

See 
 * lib/xray/dtrace/railsenable_tracing.rb
 * lib/xray/dtrace/action_controller_tracing_extension.rb
 * lib/xray/dtrace/active_record_tracing_extension.rb