speeding up debugging

I think I'm missing something.

I'm using Python 2.7 running an application under the debugger slows down the execution a lot (order of magnitude).

I have several applications with long run times (hours at full speed) that I sometimes need to break in the middle of.  I don't get why a breakpoint late in the code should effect the performance of other code.  Replace and trampoline the code at that location to jump into the debugger only when the breakpoint is hit.

I can use pdb.set_trace() and if that dropped me into the debugger I'd be happy enough.

So what am I missing?