[orban]

Yes, this correct, MySQL has to skip the first 8574 posts, that's why those queries are "slow", but they aren't that slow, really, I think. 8000 rows isn't that much (and it's fully indexed).

Yeah, adding postpos, or "page", could be a solution, but the issue is that deleting posts/moving/merging is a bit of a pain.

Worst case is that you remove the second post of a thread with 10000 replies and then you have to update 9999 rows, which is veeeeery bad. Then again you will hardly delete/move old posts in a thread and just on the last pages, where it's not a big issue to update a few dozen posts....I guess...

Mainly making sure you don't miss any actions that modify thread positions is the issue here and the problem that in certain cases you have to update many many many rows with a new postpos value.

Probably could be done just with a plugin (maybe modcp/admincp post moving options might be a problem).