[justinlloyd]

The "cache, lots of cache" statement is the most true of any MMO architecture we can build. I did some optimization work earlier this year on a project where the single back-end server is now handling 2 billion requests per minute and had around 3TB of RAM for cache (I think the final production system was aiming for 12TB of RAM).

There's concerns around race conditions as you pointed out, message passing from client to server, and server to server, client hand-off between sharded servers. Those synchronization problems will haunt your dreams.

I think the biggest issue I still struggle with is tracking those ephemeral problems that only happen on one shard, or only when going between this shard and this shard, but not the other way. One useful trick is obviously message prioritization and different messages heading to different servers - though these days I'd put a message router in front of the shards and the router handles persistent connections other than the usual technique of direct connection I've employed in the past.

Contributed to an MMO game that involves waving light sabers around, another where you defeat the ultimate prime evil (though I was more on the fraud detection on that one), an unpublished MMO that unceremoniously died during the 2008 financial crash, a "shared world" game that involved animals, an open-world game that involves driving cars and running pedestrians over, a few "internet scale" websites, and am currently lead back-end on another MMO - though our database requirements are relatively simple this time around, but it is still again, read-at-start-up, write-only-when-necessary.

[doctorpangloss]

Let's say that among developers there was a history of how-to-implement gameplay traditions (like how to implement third person player movement, "gameplay ability systems", etc.) in programming languages besides C++. Like C# & Java, the memory managed friendly ones with good tooling. And let's say you're forbidden from reinventing C++ inside C# or Java, like Unity's Burst does (so called HPC#). But you can "do ECS," there are C# and Java ECS frameworks, that even use those languages respective arena allocation techniques well. You just aren't allowed to reinvent C++, but you can use a high performance middleware that does, like Netty.

Would you choose to author an MMO backend in one of those friendlier ecosystems?

Do you think there's value in having access to other Java applications, to embed as libraries of your grander "in memory" ideas?

[reactordev]

On the backend, you aren’t limited to sub 16ms frame rates and can use languages that provide more productivity vs performance. I have infinite cloud compute, but you only have 4ghz and 16gb ram. I’ll send you highly optimized c++ and use ruby as my cloud language, it doesn’t matter.

You’ll frequently find Java, C#, Go, and Python as backend rpc/tcp game servers.

[jfim]

Interestingly enough, Jeff Kesselman was working on Java middleware for MMOs at Sun Microsystems before the Oracle acquisition. See https://en.m.wikipedia.org/wiki/Project_Darkstar

There's definitely some value in using more productive languages for the backend services, as they're not as latency sensitive as rendering.

[Stevvo]

How did they get the architecture so wrong on that "open-world game that involves driving cars and running pedestrians over"?

[dmoy]

I assume that is a tongue-in-cheek description for Grand Theft Auto (whichever one they made online). That game series has had various moral discussions / controversy surrounding it since before the first game came out like 25 years ago.

[PsylentKnight]

I assume he got that and he was referring to the jankiness of GTA Online.

For example, it took 5+ minutes to load for years, until some random guy fixed it for them [1]. Though I suppose that had little to do with the overall architecture.

[1] https://news.ycombinator.com/item?id=31681515

[Stevvo]

It uses a client-authoritative peer-to-peer architecture, which has surely led to billions in lost revenue. I'm surprised selling GTA money has done as well as it has, considering anyone could get as much as they wanted for free.

[anon56]

Not Carmageddon?

[aleph_minus_one]

> Not Carmageddon?

Carmageddon is not an MMO. :-)

[BossingAround]

Well, neither is GTA to be honest, at least not by default.

[kaliqt]

Could be APB honestly.