Are there documents on how to iterate on tables and indices? E.g. adding a new field?

We're working on it. Take a look at this page in the docs and let me know if some of the answer to your question is already there. If not, let's get those questions added and answered. https://docs.pinot.apache.org/basics/getting-started/frequent-questions

I don't think it directly answers the question. There is an answer for updating inverted indices. I'm not sure how safe 'reloadAllSegments' is. https://docs.pinot.apache.org/basics/getting-started/frequent-questions#how-to-apply-inverted-index-to-existing-setup