Asynchronous Processing for Fun and Profit

Some pro tips and an overview of Sidekiq for great async victory!

Transcript

1. Async Processing for Fun and Profit Mike Perham @mperham
2. Me Director of Engineering, TheClymb.com
3. Agenda • Basics • Protips • Sidekiq
4. Why? • User-Perceived Performance • I/O is SLOOOOOOOOOOOW • I/O is unreliable
5. What? • Optional work • Anything not required to build the HTTP response
6. How? • Client puts message on a queue • Server pulls message off queue • Worker executes code based on message
7. How? async do # perform some work end
8. How? • Marshalling a Proc • Need to serialize closure
9. How? async(instance, :method, args)
10. How? • Marshal instance • Marshal args
11. How? async(Class, :method, args)
12. How? • Serialize just the class name • Marshal the arguments
13. Congratulations! This is exactly how Resque and Sidekiq work.
14. How?
15. How?
16. How?
17. Tip #1 Small, Stateless Messages
18. Stateless • Database holds objects (nouns) • Queue holds actions (verbs) • “Perform X on Object 123”
19. Avoid State • Bad • @user.delay.sync_images • Good • User.delay.sync_images(@user.id)
20. Simple Types • Small & Easy to read • Cross-platform • Sidekiq / Resque use JSON
21. Debugging
22. Tip #2 Idempotent, Transactional Units of Work
23. Idempotent • Fancy computer science term • “Work can be applied multiple times without changing the result beyond the initial application”
24. Idempotent • Canceling an order • Updating user’s email address
25. Not Idempotent! • Charging credit card • Sending email
26. Idempotent • Your code has bugs! • Sidekiq will retry jobs that raise • Design jobs to be retried • e.g. verify you need to perform action before performing it
27. Transactional • Infinite credit?
28. Tip #3 Embrace Concurrency
29. Concurrency • Resque/DJ = 4 workers • Sidekiq = 100 workers • Mike, what is best in life?
30. “To crush their servers, see them smoking before you and hear the lamentations of their admins.”
31. Concurrency • Use connection_pool gem to limit client connections • Split work into small batches • 100 items => 10 jobs of 10 items
32. Concurrency • Thread safety rarely an issue • Most gem maintainers very responsive • Recently fixed: • cocaine, typheuos
33. Theory, meet Practice
34. Sidekiq • Simple, efficient message processing • Like Resque, but 10x faster
35. MODERN RUBY IS NOT SLOW SINGLE THREADING IS SLOW
36. Concurrency • To scale single-threaded, create lots of processes. • HORRIBLY RAM INEFFICIENT
37. Threads vs Processes • Example: 400MB single-threaded process • 25 processes = 10GB RAM = EC2 xlarge • 25 threads = 1GB RAM = EC2 small • $60/month vs $480/month • 160 dynos => 10 dynos • 150 dynos * $35/month =~ $5000/month
38. Quick Rant • GIL + poor GC • C extension API must DIE • What’s larger: 50% or 800%?
39. Client Your App Client Middleware Redis Sidekiq Client API Rails Process
40. Server Processor Server Middleware Redis Worker Sidekiq Process Processor Server Middleware Worker Processor Server Middleware Worker Processor Server Middleware Worker Fetcher Manager
41. Versions • Sidekiq - Free, LGPLv3 • Sidekiq Pro - more features, support, $ • motivation!
42. Features Sidekiq Resque DJ Concurrency Store Hooks Web UI Scheduler Retry Delay Batches Threads Processes Processes Redis Redis DB middleware callbacks callbacks ✓ ✓ ? ✓ ? ✓ ✓ ? ✓ ✓ ? ✓ Pro ? - ? - optional
43. Future • Nicer, more functional Web UI • APIs for managing queues / retries • Rails 4 Queue API
44. Pro Future • Enterprise-y features • Workflow • Notifications
45. Conclusion • small, stateless messages • idempotent / transactional • concurrency • sidekiq
46. Questions? @mperham mperham@gmail.com