Hey sorry just saw this. Yep like fiatjaf said, these are the index definitions:

https://github.com/hoytech/strfry/blob/master/golpe.yaml#L24-L47

Just below is the indexPrelude, which is the code that actually populates those indices.

The querying is most in the DBQuery file here: https://github.com/hoytech/strfry/blob/master/src/DBQuery.h

But it's not really well document or obvious. In general, there are some rough heuristics about which index to use, and then does a scan of that, only loading the actual event data if needed (sometimes it can satisfy the query with index-only). Here are some basic docs in the README:

https://github.com/hoytech/strfry?tab=readme-ov-file#database

Happy to try to answer any specific questions if you have them.