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You ain't gonna need write a GenServer - Ulisses Almeida | Elixir Club Ukraine
- 1. You ain't gonna need to write a GenServer by Ulisses Almeida
- 2. Summary ■ What is GenServer? ■ How can you harm your app by putting GenServer in the wrong place? ■ Why do people think that they need a GenServer all the time? ■ Considerations before writing a GenServer
- 3. I’m Ulisses Almeida ■ Elixir Developer at The Coingaming Group ■ @ulissesalmeida
- 4. Why Tallinn? ! ★ Low renting costs ★ Free transportation for residents ★ E-estonia 💻 ★ Safe ★ Low taxes ★ Accessible travels ๏ Cold and Dark ☃ ๏ Estonian is the first language ! ๏ Russian is the second language $ ๏ Eastern/nordic culture is different
- 5. Learn Functional Programming with Elixir ■ 20% off with Elixir_Ukraine_2019 promo code
- 6. Who We Are The Coingaming Group are the crypto gaming pioneers who operate the world’s leading bitcoin gaming and betting brands. https://coingaming.io/
- 7. Ok, GenServers A quick recap
- 8. https://twitter.com/ulissesalmeida/status/1125455706470088704
- 9. GenServer ■ Useful for: Client-Server relationship ■ Keep state ■ Execute code asynchronously (handle_cast) ■ Synchronously too (handle_call) ■ Provide tracing and error reporting features ■ Can be supervised A process with a powerful set of features
- 10. Shades of a GenServer ■ Agent ■ Task ■ Task.Supervisor ■ Supervisor ■ DynamicSupervisor ■ GenStage ■ …
- 11. CalculatorServer Baby 1+1? 1. 2. 3. From: Baby 1+1? 4. 1+1=2 5.
- 12. CalculatorServer Baby 7. 6. From: MyCalcGenServer 2 8.
- 13. Live demo “…maybe I should have recorded a video”
- 14. Wut!?
- 15. hahahahah GenServer bottleneck omg what I have done!?
- 16. Holy %#@! ~ 200 times slower ~ 10 times more memory 120km/h 1.6km/h ~75 times slower 10 times bigger
- 17. What happened!? 🤔
- 18. CalculatorServer AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAA
- 19. Without GenServer… 🤔
- 20. CalculatorServer
- 21. CalculatorServer ☠🔥 🔥 🔥 🔥 Omg the server is on fire! !
- 22. Why people want it so much? Can we play just with functions?
- 23. Erlang OTP ■ Process hierarchy ■ Restarting strategies ■ Concurrency ■ GenServer plays the central role
- 24. wait, you said concurrency…🤔
- 25. GenServer checklist ■ Model state accessed by multiple processes ■ Run multiple tasks concurrently ■ Communicate between servers ■ Gracefully handle clean startup and exit concerns https://pragprog.com/book/tvmelixir/adopting-elixir
- 26. CalculatorServer checklist ❌Model state accessed by multiple processes ❌Run multiple tasks concurrently ❌Communicate between servers ❌Gracefully handle clean startup and exit concerns https://pragprog.com/book/tvmelixir/adopting-elixir
- 27. CalculatorServer has no reason to be a GenServer A GenServer must never be used for code organization purposes https://hexdocs.pm/elixir/GenServer.html GenServer to organize domain, business contexts GenServer to model runtime properties of your system
- 28. Fear of missing out? Am I a proper Elixir developer If I'm not doing GenServers?
- 29. I have been working with Elixir for ~3 years ■ I hardly often write a GenServer ■ I mostly wrote GenServers in recruitment processes and for fun ■ I deleted some unnecessary production GenServers ■ I know excellent developers that never wrote one
- 30. Elixir developers, no shame in never had to create a GenServer.
- 31. Ecosystem got you covered Or… things that you should consider before writing a GenServer
- 32. Let's think about a typical web application
- 33. Phoenix Elixir Database Legacy Legacy of the Legacy Users
- 34. Users & App
- 35. Users -> App checklist ✔ We need to handle multiple users connections concurrently ✔ Other processes might send messages to that connection ✔ We have to handle connections openings and closings gracefully.
- 36. GenServers!
- 37. However… ■ Each user’s request has a process that runs concurrently ■ You can focus on the functional part ■ (functional part? functional programming 🥁) Phoenix and Cowboy handles that for you
- 38. App & Database
- 39. App & Database checklist ✔Databases are an external service communication ✔We have to provide a limited number of connections to a lot of processes ✔These connections have to run concurrently ✔We need to handle connection openings and closings gracefully
- 40. GenServers!!!!
- 41. However… ■ Ecto supports a pool of connections ■ Ecto handle that concurrently ■ Work here is also done ■ You can focus on the business 💰Ecto handles that for you
- 42. App &Other Services
- 43. App & Other Services checklist ✔ Usually, we communicate through a network ✔ We might need to offer a pool as a backpressure mechanism to not bring down weak services ✔ These pools have to run multiple requests concurrently ✔ Gracefully handle connections opening and closings
- 44. GenSeerveerss!!!
- 45. However… ■ You can start simple, for example, no pool ■ Watch out for big timeouts ■ Circuit breakers can help you out ■ Choose the libraries, and you can focus on features Hackney and other libraries handles that for you
- 46. NoSQL storage
- 47. Not everything is stored in SQL databases ■ Examples: caching, session, users presence ■ Transient or Persistent? ■ How big will it be? ■ Write vs Read ✔ This data will be accessible by multiple processes
- 48. GenSeeerveerS!!!!!
- 49. WITH ETS!!!!!!!
- 50. Phoenix ElixirElixir ETS table Phoenix Elixir ETS table Phoenix Elixir ETS table User
- 51. However… ■ A better abstraction reveals intention, for example, Cachex vs GenServer + ETS ■ How does your deploy work? ■ Shutdown and booting the app will lose GenServer/ ETS data ■ Redis for the rescue ■ Discuss the right tool for the job, compare the tradeoffs You might want to use a specific abstraction.
- 52. Serializable operations
- 53. Serializable operations Some resources can’t be changed at same time 1 1 5 I want to withdraw 2 I want to withdraw 6 Company Wallet ✔ Manage state accessed by multiple processes
- 54. …GenServer?
- 55. However… ■ You would need an Erlang cluster to run a global GenServer ■ What happens with network partition? ■ Use your database power ■ Transactions or locks in the database ■ Discuss with your team, compare the tradeoffs You environment might not allow. a.k.a Heroku
- 56. Background tasks
- 57. Tasks outside of a request/response cycle ■ Welcome e-mail ■ Push notifications ■ Scheduled tasks ✔ We need to spawn or schedule these background tasks ✔ We need to run the background tasks concurrently
- 58. Dynamic Supervisors & Task!!!
- 59. However… ■ GenServers aren’t persistent ■ Shutting downs might lose data ■ RabbitMQ has persistent queues ■ Libraries that use Redis to store the jobs and their arguments ■ Discuss with your team, compare the tradeoffs How to handle the failures? Do you need some persistence?
- 60. We covered a lot of considerations before “let's write a GenServer” decision And they are still not over
- 61. GenServers are fundamental
- 62. Elixir frameworks and libraries cover most of the use cases that you would need to write one
- 63. But it doesn’t mean you should not learn about GenServer
- 64. You need to know GenServer to tune their configurations
- 65. When stuff goes wrong, you’ll need to debug and fix it.
- 66. You won’t might need to write a GenServer 95% of time…
- 67. But that 5%…
- 68. Then, keep learning!
- 69. Remember
- 70. Putting a GenServer in the wrong place brings more harm than good
- 71. It’s good to compare and to discuss the tradeoffs with your team.
- 72. There’s no shame in never need to write a GenServer
- 73. Thank you
- 74. References ■ Adopting Elixir - https://pragprog.com/book/tvmelixir/adopting- elixir ■ Spawn or not spawn - https://www.theerlangelist.com/article/ spawn_or_not ■ You may not need a GenServer - https://pragtob.wordpress.com/ 2019/04/24/you-may-not-need-genservers-and-supervision-trees ■ GenServer (Elixir Docs) - https://hexdocs.pm/elixir/GenServer.html ■ Elixir discussion forum - https://elixirforum.com/t/you-may-not- need-genservers-and-supervision-trees/12947
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