holli suggested marking replies newer than the last time the user clicked "I've checked all of these". That's radically different from almut's suggestion to mark replies which have been added since the thread was last visited.

tye only struct down almut's suggestion, not holli's. It's tye's post that needed rereading.

holli's suggestion is actually quite cheap. All that's needed is to fetch the RAT/NN timestamp associated with the user (which could be fetched at the same time as other user info is fetched) and the timestamp of every post (which is already fetched).

almut's suggestion would require creating a new timestamp for every thread every user visits and fetching numerous timestamps everytime a thread is displayed.