is membase a good persistence layer for a erlang gamer server?

Question

I aim to create a browser game where players can set up buildings.

Each building will have several modules (engines, offices,production lines, ...). Each module will have enentually one or more actions running, like creation of 2OO 'item X' with ingredients Y, Z.

The game server will be set up with erlang : An OTP application as the server itself, and nitrogen as the web front. I need persistence of data. I was thinking about the following :

When somebody or something interacts with a building, or a timer representing some production line ends up, a supervisor spawns a gen_server (if not already spawned) which loads the state of the building from a database, so the gen_server can answer messages like 'add this module', 'starts this action', 'store this production to warehouse', 'die', etc. (

But when a building don't receive any messages during X seconds or minutes, he will terminate (thanks to the gen_server timeout feature) and drop its current state back to the database.

So, as it will be a (soft) real time game, the gen_server must be set up very fastly. I was thinking of membase as the database, because it's known to have very good response time.

My question is : when a gen server is up an running, his states fills some memory, and this state is present in the memory handled by membase too, so the state use two times his size in memory. Is that a bad design ?

Is membase a good solution to handle persistence in my case ? would be use mnesia a better choice , or something else ?

I fear mnesia 2 Go (or 4 ?) table size limit because i don't know at the moment the average state size of my gen_servers (buildings in this example, butalso players, production lines, whatever) and i may have someday more than 1 player :)

Thank you

Answer 1

I agree with Hynek -Pichi- Vychodil. Riak is a great thing for key-valye storage.

We use Riak almost 95% for the same thing you described. Everything works so far without any issues. In case you will hit performance limitation of Riak - add more nodes and it good to go!

Another cool thing about Riak is its very low performance degradation over the time. You can find more information about benchmarking Riak here: http://joyeur.com/2010/10/31/riak-smartmachine-benchmark-the-technical-details/

In case you go with it:

• a driver: https://github.com/basho/riak-erlang-client
• a connection pool you may need to work with it: https://github.com/dweldon/riakpool

About membase and memory usage: I also tried membase, but I found that it is not suitable for my tasks - (membase declares fault tolerance, but I could not setup it in the way it should work with faults, even with help from membase guys I didn't succeed). So at the moment I use the following architecture: All players that are online and play the game are presented as player-processes (gen_server). All data data and business logic for each player is in its player-process. From time to time each player-process desides to save its state in riak.

So far seems to be very fast and efficient approach.

Update: Now we are with PostgreSQL. It is awesome!

Answer 2

You can look to bitcask or other Riak backends to store your data. Avoid IPC is definitely good idea, so keep it inside Erlang.