CODEWITHSUNDEEP
erlang
Not an ID
Not an ID

Reputation: 2589

How to implement status in Erlang?

I am thinking an Erlang program that has many workers (loop receive), these workers almost always manipulate their status at the same time, ie. massive concurrent, the amount of workers is so big that keep their status in mnesia will cause performance problem, so I am thinking pass the status as args in each loop, then write to mnesia some time later. Is this a good practice? Is there a better way to do this? (roughly speaking, I'm looking for something like an instance with attributes in the object oriented language)

Thanks.

Upvotes: 1

Views: 97

Answers (1)

Pascal
Pascal

Reputation: 14042

With Erlang, it is a good habit to see the processes as actor with a dedicated and limited role. With this in mind you will see that you will split your problem in different categories like:

  1. Maintain the state of a connection with a user over the Internet,
  2. Keep information such as login, user profile, friends, shop-cart...
  3. log events
  4. ...

for each role you will have to decide if the state information must survive to the process.

In a lot of cases it is not necessary (case 1) and the solution is simply to keep the state in the argument of loop funtion of the process. I encourage you to look at the OTP behaviors, the gen_server and gen_fsm are made for this.

The case 2 obviously manipulates permanent data which must survive to a process crash or even a hardware crash. These data will be stored using dets, mnesia or any database adapted to your problem (Redis, CouchDB ...).

It is important to limit the information stored into external database, otherwise you will not benefit of this very powerful feature which is the lack of side effect. In other words, it is a very bad idea to have process behavior which depends on external information.

Upvotes: 1

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