When hundreds of players hit one boss at the same time, the computation for that single boss piles up in one place, and hit information goes out to everyone watching.
Why Hundreds of players use skills, buffs, and debuffs on one boss nonstop → Effect The boss’s HP, aggro list, and debuff calculations pile up in one place, and every hit sends damage number and effect packets to everyone watching → On screen Skills land late and damage numbers pop up in bursts; slow motion only around the boss
Bundle or skip other players’ damage numbers and effects, cap the number of debuffs on one target, split hit processing across several ticks.
Ballpark numbers
800 players hitting twice a second makes 1,600 hits per second. Telling all 800 watchers about every hit means 1.28 million messages per second.
On the graph
Rises with load · Server tick time, messages sent
Where to look
Tick time and packets sent during the boss fight, alongside the number of players around the boss, plus events per second (hits, buffs, debuffs) per target if available
Confirmed if
As players gather around the boss, tick time and outbound traffic climb steeply, and the boss alone has tens of times more events per second than any other target
Ruled out if
Things slow down just as much whenever players gather, boss or no boss: points to “AOI calculation blowup (N²)” or “Broadcast fan-out overload”
Check with
Game server or client logs and metrics
Sources
HED-GP Technical Retrospective: What a HED-acheCCP Games Even a single attack must be reported to every client watching, creating an O(n²) load of n players notifying n players, and message-heavy drone attacks make this load grow even faster