Erlang MMORPG Engine

http://www.next-gen.cc/

by flashingpumpkin • 17 years ago

64 37 17 years ago

next-gen.cc

erikwiffin• 17 years ago

This is timely, as I've started working on an MMO as a side project.

Of note: I think your wiki has been hacked.

flodihn3• 17 years ago

Yeah recently noticed, I fixed that now.

conflux0• 17 years ago

Interesting stuff. Although you might want to get rid of the large background image crowding out the content on your site.

Periodic2• 17 years ago

I'm on a laptop with a wide screen and it took me a moment to realize that the navigation links worked, I just had to scroll down to see anything different.

revoltingx2• 17 years ago

Cool, I've been waiting for something like this to sprout out. I've been working on something similar, haven't yet looked at the code, but I wonder how well it scales as far as number of users, since Mnesia supposedly doesn't support very large tables. For this reason I chose to use PostgreSQL for things like areas, characters, items, etc. Because it's easier to shard and has a stable track record. However, for soft-realtime data (like area co-ordinates, velocity, etc.) in-memory Mnesia/ETS is the way to go.

troystribling2• 17 years ago

Menasia tables are limited to 4GB on a 32bit OS but can get to 16 exabytes on a 64bit OS, p 294 Programming Erlang, http://books.google.com/books?id=Qr_WuvfTSpEC&pg=PT1&...

troystribling2• 17 years ago

disc-only copies are actually limited to 2GB, so available RAM will place a limit on DB size.

From Programming Erlang,

For massive numbers of entries that you want to be able to access readily, you might be better off using CouchDB, MySQL, PostgreSQL, or Berkeley DB, all of which have open source Erlang drivers and APIs available. The upper limit of a Dets table is 2 GB. This means the upper limit of a Mnesia table is 2 GB if the storage type is disc-only copies. For other storage types the upper limit depends on the system architecture. In 32-bit systems the upper limit is 4 GB (4 * 109 bytes), and in 64-bit systems it is 16 exabytes (16 * 1018 bytes).

flodihn3• 17 years ago

I use Mnesia mostly to store temporary distributed data. If you want to store persistent data with another database you can just replace the implementation module for libsave with your own. libsave is my library for storing objects to disk.

So far I don't know how many users my servers scales to, with some rough test I can have about 2000 players in the same spot, I recently added a quad tree and with that in place I hope that will increase a lot if players are spread out in the area.

vito• 17 years ago

I've been working on a server for Ragnarok Online in Erlang if anyone's interested: http://github.com/aliter/aliter . It's structured similarly I suppose, except it has no monitoring server. Players are represented as gen_fsms, and the servers (login, char, and all the zone servers) can be distributed across various nodes, etc. It uses Mnesia for its database, and the scripting language will likely be lfe or Reia. (It's lfe at the moment, but if Reia evolves enough we may jump over to that.)

Unfortunately as I'm reimplementing a server for a client that already exists, I had to offload some of the time-sensitive stuff onto C as it's simply too slow in Erlang (in this case, walking + pathfinding).

Edit: Also, hot code loading is f'ing incredible for stuff like this. Get on, walk a bit, notice a bug, update it in the code, make:all([netload]) in the shell, bam, fixed. (Though I had to patch stdlib to fix a bug in c:nc that makes make:all([netload]) useless. I've submitted a patch and it's in the pu branch.)

steamboiler2• 17 years ago

I recently got introduced to Erlang and have a question. How do you unit test your code? I recall reading that the CouchDB author was obliged to use JavaScript for automating his unit tests. What was your experience?

roder• 17 years ago

Look at eunit

evgen2• 17 years ago

eunit is good for simple functional tests (etap is another option here) but it is not really sufficient for testing things like gen_servers and more complex behavior. OTP includes a testing framework (common test) that does these sorts of tests and is in fact used to test the rest of OTP, but it is a PITA to configure and documentation is rather thin so most people opt for low-level eunit tests and hope for the best when it comes to the more complicated bahaviors of the system...

anigbrowl• 17 years ago

I appreciate the succinct blog discussion of past failures: http://www.next-gen.cc/index.php?option=com_content&view...

jerf2• 17 years ago

Yeah, that's a nice link.

I feel like I'm spamming this point sometimes, but I don't think it can be said enough: If you are a language designer and you want to displace Erlang, you shouldn't be targeting "shared-nothing concurrency" or "message passing"; those are merely the door fee. OTP is what you need to replicate/replace/supplant. All of it, including the cross-machine stuff. Believe me, there's room for improvement.

aaronblohowiak• 17 years ago

can you please elaborate on what you'd like to see improved in OTP?

EvilTrout4• 17 years ago

I'm probably going to use Erlang for the server side component of my next MMO (I created Forumwarz, a web based MMO in Ruby on Rails.) So this was a very interesting find.

It's curious that the author uses TCP. Almost every high performance game uses UDP, as you don't care about lost packets or the order 99% of the time. You just want the latest information.

One reason might be to use Flash for the front end. It does not allow UDP sockets at this time.

simplify• 17 years ago

TCP vs UDP is a hot debate. It really depends on the type of game you're trying to build.

http://www.gamedev.net/community/forums/topic.asp?topic_id=3...

As an interesting note, World of Warcraft uses TCP.

oconnor0• 17 years ago

Does WoW use TCP for all communication?

EvilTrout4• 17 years ago

Wow, very interesting thread. I read the whole thing and stand corrected.

patio112• 17 years ago

So if I were very hypothetically having recurrent dreams of making my next Rails app a game, what would you tell me to bring me to my senses?

EvilTrout4• 17 years ago

It depends what kind of game you're creating. For the kind of game we built it was a huge win. Some of the features were deployed in days.

Ruby might be slow, but in my experience as long as you give it a lot of RAM to play with it can give you great performance (we have over 200k registered players). Of course, we also cache data heavily using memcached.

bilbo0s• 17 years ago

Does anyone know what doing physics in Erlang is like on the zone or area servers? Or do most people just not do physics?

I would think that the physics is what makes things difficult. Of course, if you can think of a game where physics simulations are not as important, an Erlang engine really starts to make sense. At least that is my impression. I'd really be interested in hearing from anyone who has had experience with physics in Erlang.

forensic• 17 years ago

physics rarely matters for MMOs. The biggest MMOs like wow have almost no physics at all - just gravity and occasionally a single force vector being applied to a perfectly rigid, non-rotating object in a frictionless environment.

Periodic2• 17 years ago

It seems that most MMOs, at least of the fantasy variety, tend to ignore physics. Mobiles have maybe three speeds, stopped, walking, and running and transition instantly between them. Jumping is just a pre-programmed arc that may have checks for colliding with other objects. Fall speed tends to be constant and non-accelerating.

However, space-based games would likely require a little more physics to be interesting.

revoltingx2• 17 years ago

Although I haven't gotten to that part of my game server, I've tried to design it to avoid any sort of physics, because of the potential latency between a client and the server. (I'm targeting mobile users.)

The only 'physics' that need to be calculated is when a player changes speed/direction, and you must calculate the path and detect collisions.

However, to minimize negative effects on gameplay, both the client and the server 'dead reckon' the position of players in their immediate view bubble.

In the client, this is done on a separate thread, on the server, a separate set of processes. Again, I don't expect my algorithms to be cpu heavy, but if they were I'd probably implement them in C and communicate with the erlang processes via message passing. However, this may not be feasible if the latency is too much, in that case, C/C++ is probably more apt. However, you'd have to implement your own scaling, so I'd rather modify my game design than write the functionality that erlang already provides.

grogers• 17 years ago

What gui is that on the videos that shows the supervisor tree?

flodihn3• 17 years ago

The GUI showing the supervisor tree is the appmon application, it comes with erlang. You can start it by typing appmon:start() from the erlang shell.

perplexes• 17 years ago

There are more videos here: http://www.youtube.com/user/flodihn

Erlang MMORPG Engine

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