How do you evaluate a RAG system’s performance when the answer is not present in the retrieved documents? (Does it correctly say "I don't know"?)

How do you measure "Time to First Token" (TTFT) vs. "Total Runtime"? Which one matters more for user experience in a chatbot?

If you are using an LLM to grade another LLM, why is it critical to provide a "multi-point rubric" rather than just asking "Is this answer good?"

What is the difference between testing your model on a static CSV file (Offline) vs. monitoring real user "Thumbs Up/Down" feedback (Online)?