"On Saturday morning Pacific timing, we suffered a global outage due to an abrupt, massive increase in traffic. This was a new level which our servers had never had before, since the beginning of the game," Blizzard explained with D2R Items.This was further exacerbated by an upgrade we'd released earlier in the day with the intention to improve the performance of games during creation. Both factors together overloaded our global database, causing it to be delayed. We took the decision to roll back that Friday update we'd previously deployed in the hope of easing the load on the servers going into Sunday and also giving us the space to explore the root of the problem.
On Sunday, though, it became clear what we had done on Saturday was not enough. On Sunday, we saw a much greater rise in traffic that caused us to hit another outage. Our game servers had noticed the database's absence and attempted to reconnect repeatedly, which meant the database did not have the time to finish the work we had completed because it was dealing with a constant stream of connecting attempts from game servers. We also discovered that we could enhance our configuration for database event logging, that is required to restore an appropriate state in the event the database fails, so we completed those, as well as a deeper root cause analysis.
This isn't exactly the recipe for having a great time, that. It's also why players had several issues with the game's progress. You'd choose your character, begin a game after which you would play for a time but the regional server couldn't communicate with the central database after an outage. This meant it wasn't able to tell Diablo 2's the source in "ground truth" about the brand new equipment and XP that you'd accrued, resulting in frustrated players losing some of the progress they'd made.
The issue only got more serious as time went on. It was a long time since the Diablo 2 servers came back on the internet, but they were not online during a time when most players were online--so although the servers re-established rapidly, they crashed nearly immediately when several hundred thousand Diablo 2 instances fired up.
If the weekend went badly but what came next on Tuesday and Monday was not much more bleak: This leads us to Monday, October 11 and the switch from the global databases with Diablo 2 Resurrected buy items. This caused another outage in which our backup database was incorrectly continuing to run its backup process. This meant that it was spending the majority of its time trying to copy its data to the second database when it was supposed to handle the requests of servers.