Document performance degradation running under debugpy when not attached

[jkugler]

Given a use case such as this:

exec /.venv/bin/python3 -m debugpy --listen 0.0.0.0:5678 ${DEBUG_CMD} -m uvicorn --reload --host "$HOST" --port "$PORT" --log-level "$LOG_LEVEL" "$MODULE_NAME"

it would be nice to know how much of a performance hit we're getting by starting our code under debugpy, but not attaching to it. I've come across a situation where we might be running our code under debugpy in production, and I want to know how much this is hurting us. This does not seem to be covered by the current documentation.

[rchiodo]

Not an issue, transferring to Q&A

[rchiodo]

I can tell you what we do before you actually attach:

• Setup a trace callback using either sys.settrace or sys.monitoring. (3.12 we switched to sys.monitoring)
  • Sys.monitoring should be a lot faster because until we enable tracing (when you attach), it doesn't actually call us
• Setup a hook to watch thread creation
• Open a socket running on another thread to listen for messages
• Create another process that listens on the port you specified (it's called the adapter process)

How long each of those things takes, hard to say.