Blizzard Developer on Sharding, Layers, and The Blood Moon Event - Season of Discovery

19.02.2024 - 00:59 / wowhead.com

Blizzard Developer Tom Ellis shared some interesting insight on Twitter covering the history of Sharding, Layering, and how layering issues are working on being resolved. Many players have been sharing negative experiences with layering during the Blood Moon Event in Stranglethorn Vale on Season of Discovery, hopefully a fix will be implemented soon.

Tom Ellis

Once upon a time, a realm ran one copy of each zone locally on it's own hardware, if you ran after someone and they crossed into another zone, you followed them, it was all running in the same place, you could kite mobs across zones, escort quests had NPCs pathing across zone boundaries.

Problem, as hardware improved and performance improvements were made, expansion after expansion we raised the cap on the number of concurrent players we allowed logged in. If everyone wants to play on Tich, and we have the technical capacity to lower queue times, why wouldn't you? Ah, but the realm still only ran one copy of the world, eventually the realm has so many people on it that if even a small percentage of them congregate in the same place its going to be way more than the CPU core that's running that zone can handle, in comes the lag, you can multithread to your hearts content, eventually you're going to have a single thread bottleneck that will limit what you can do.

This all came to a head in Warlords of Draenor when in the face of a very successful launch the starting zones in WoD were completely unable to handle the load they faced.

The sadly departed @kurtismcc (not dead, just left Blizzard...) worked for three days and nights (we don't condone that sort of behavior anymore!) and created the first version of sharding, this new tech allowed us to run multiple copies of the world and split people between them. Finally we could run multiple copies of Draenor and handle the load between them.

With Legion this tech was made into a fully fleshed out feature and each individual zone could now run limitless copies, once a threshold of players in the zone was reach, we spun up another copy, repeat as necessary.

It made the game feel less cohesive, but it meant the realm cap and zone capacity were now disconnected entirely, it also gave us the ability to have specific values for specific zones (not all zones are equal in terms of CPU cost).

Good times. Now, along comes Classic and we have problems again.

Classic launch was heavily targeting #NoChanges, they wanted the game to feel.