Over the last couple of years, we've begun using some new technology we've occasionally referred to as "sharding" in non-instanced zones, which separates players in high-traffic areas out into separate "shards" of a particular zone. The benefit to our server performance has been massive - it was a huge part of why Legion's launch went so smoothly - and so, as a whole, we've been very happy with the system.
The one exception has been on RP realms, where player-run events are much more common. On RP realms, we believe that the overall loss to game performance is worth it in order to support those events. If players on RP realms choose to organize an event and congregate somewhere, and have a laggy experience as a result, that's their choice, and we'd like to allow them as much freedom to do so as possible.
So, we've recently applied a hotfix that should disable realm sharding in the vast majority of the outdoor world on RP realms. That includes Kalimdor, the Eastern Kingdoms, Northrend, Pandaria, Outland, Draenor, and all related sub-zones. This has actually been our intention for some time now, but as part of investigating some reports involving a player-run event in Northrend, we discovered some secondary issues that were causing it not to function properly.
There are still limits, of course; we don't want playing on an RP realm to mean you can't properly experience core game content due to low FPS or heavy input lag. As such, all Legion zones (including all of the Broken Isles, the Broken Isles version of Dalaran, and soon, Argus) will still have sharding active, as they do on non-RP realms. Similarly, when the game itself points players toward a specific area of the non-Legion world (such as for a holiday event or new patch content), we may temporarily re-enable sharding in that area until things settle down.
In general, however, our goal is to follow the general rule of thumb that RP realms do not shard, except in current-expansion zones, or when temporarily necessary to support gameplay. This should now be the case on all RP and RP-PvP realms worldwide. This is in addition to our existing rule that RP realms do not automatically fill areas using our Cross-Realm Zones system (although you can still enter an RP realm using CRZ if you're grouped with a player on an RP realm).
Thanks for all your patience while we implemented the hotfix on this, and awesome job on the Tournament of Ages, guys! :)
What about cities ?