Those are well reasoned points. I'm not going to delve into STM because that can be a whole book worth of discussion :). It's a fascinating universe, I've spen

Those are well reasoned points. I'm not going to delve into STM because that can be a whole book worth of discussion :). It's a fascinating universe, I've spent many hours (weeks, months?) exploring it, and I don't consider myself even close to an expert. You are absolutely correct about the trade-off about atoms in Clojure. Practically speaking, to start seeing retries you'd have to have a big number of updates going on at the same time. You can push a huge number of updates through a single thread. If you do have the need to do big throughput, you can explore not-so-idiomatic options like atoms-in-atoms, like you said. IMO, the biggest unique benefit of combining atoms with immutable persistent data structures, comes from the fact that you can get unlimited number of consistent readers virtually for free. Any thread can look at (aka, deref) an atom, while the state/world keeps moving forward. I don't think any amount of tooling can solve that case for mutable data. A snapshot of a mutable data structure would require copying the whole data structure while using some sort of a locking strategy to stop writers while the read is taking place.