Blizzard says it had "a couple of hundreds of thousands of D2R Items players in one region alone"--which could be quite a lot or fairly standard, depending on how Blizzard's servers define the regions. (A small number of hundred thousand could be impressive for such a place as Australia.
For an "region" such as in the United States, not so much. However, if that area was only a tiny portion within the United States, then maybe it could be. The blog post doesn't provide any specifics this. )According to the developers.
One of the biggest issues to be found in this is how the original Diablo 2 handles core pieces of player behavior. As Vicarious Visions updated the original D2 code where they could, the biggest part of the game was keeping the code that was working.
Which was fine, up until the point that it didn't begin to grow.
Diablo 2 has a particular method for pulling data from the central database to ensure that players are able to do the things they'd like to accomplish. You're playing? This is calling back to the database central.
You'd like to switch your character? You can also check central command to make sure your character is the one you wanted, in the same spot that you left it and with everything you'd put in for.
Diablo 2, according to the team, was created as a centralized service. The disadvantage of this is that only a single instance of this particular service can be run at any time, which means they cannot transfer some of the workload to servers in regional locations.
"Importantly the service is a singleton, which implies that we will only be able to run just one instance to ensure that each player has access to the most recent and correct game list constantly," the devs wrote. "We did optimize this service in several ways to conform to more technologically advanced technologies, but as we previously mentioned most of our issues are due to games being created."
There's currently a number of options for short-term solutions as well as plans to revamp D2R items cheapstructure so that it's better able to meet the current demands. The service that offers a list of games to players, for instance is now being restructured into a separate service that is its own.