[joshuak]

Distributed consensus is hard. Very hard. Anyone dismissing the problem as “should never have hopped,” hasn’t a clue as to how hard and error prone reliable distributed consensus is. 35 ms lag in overall responsiveness is an eternity in competitive game play.

There are videos floating around that show drawing on a tablet surface with various input latencies (perhaps someone has a link, I can’t find them at the moment). 35ms latency is very noticeable to anyone never mind professional competitors.

Because of the tricks game designers must pull off in lieu of proper distributed consensus which has hard requirements bound by the laws of physics, it is completely likely there are lots of bugs in the system. I think Riot did the best anyone could reasonably have expected of them, and the write up is particularly informative and helpful.

[namibj]

I think you meant https://youtu.be/vOvQCPLkPt4 . It was indeed not too easy to find, due to SEO tactics polluting YT search with gaming-oriented stuff from recent times (where one may actually reach the frame rates necessary for such low latencies in a frame-by-frame display technology).

[joshuak]

Thanks! That is the one I was thinking of. Notice how even at 10ms of latency rubberbanding is easily visible.

[joebob42]

There's no consensus involved in the bug.

[joshuak]

Sure there is. The need to introducing a unified delay across all game clients in the first place, reliable measurement and comparison of latency data, and the effects of latency, artificial or otherwise, on game state which is not strongly consistent. There could be many other areas in which this bug intersects with distributed consensus in the actual implementation as well.

In fact neglecting the impact of distributed consensus is one of the biggest challenges to mitigating it.