Sagas: Distributed Transactions Without Locks

This talk discusses the sagas pattern and an Erlang implementation of the pattern from Erlang User Conference 2017

1. Sagas: distributed transactions without locks in Erlang MARK ALLEN - ALERTLOGIC MARK.ALLEN@ALERTLOGIC.COM @BYTEMEORG
2. Sagas
5. Types of Sagas §Backward Recovery §Forward Recovery §“Recovery Blocks” §Parallel Sagas
6. Sagas in Erlang
7. The Big Idea Fold over a list of closures…
8. The Big Idea Fold over a list of closures… ...unless there’s an error.
9. The Big Idea Fold over a list of closures… ...unless there’s an error; Then, fold over a list of closures.
10. Flows Forward 1 Forward 2 Forward 3 Forward 4 Forward 5 Rollback 1 Rollback 2 Rollback 3 Rollback 4 Rollback 5
11. Flows Forward 1 Forward 2 Forward 3 Forward 4 Forward 5 Rollback 1 Rollback 2 Rollback 3 Rollback 4 Rollback 5
12. Flows Forward 1 Forward 2 Forward 3 Forward 4 Forward 5 Rollback 1 Rollback 2 Rollback 3 Rollback 4 Rollback 5
13. Flows Forward 1 Forward 2 Forward 3 Forward 4 Forward 5 Rollback 1 Rollback 2 Rollback 3 Rollback 4 Rollback 5
14. Flows Forward 1 Forward 2 Forward 3 Forward 4 Forward 5 Rollback 1 Rollback 2 Rollback 3 Rollback 4 Rollback 5
15. Flows Forward 1 Forward 2 Forward 3 Forward 4 Forward 5 Rollback 1 Rollback 2 Rollback 3 Rollback 4 Rollback 5
16. Flows Forward 1 Forward 2 Forward 3 Forward 4 Forward 5 Rollback 1 Rollback 2 Rollback 3 Rollback 4 Rollback 5
17. Flows Forward 1 Forward 2 Forward 3 Forward 4 Forward 5 Rollback 1 Rollback 2 Rollback 3 Rollback 4 Rollback 5 BOOM
18. Flows Forward 1 Forward 2 Forward 3 Rollback 1 Rollback 2 Rollback 3 BOOM
19. Flows Forward 1 Forward 2 Forward 3 Rollback 1 Rollback 2 Rollback 3 BOOM
20. Flows Forward 1 Forward 2 Forward 3 Rollback 1 Rollback 2 Rollback 3 BOOM
21. Flows Forward 1 Forward 2 Forward 3 Rollback 1 Rollback 2 Rollback 3 BOOM
23. Terminology §Operation §Step §Transaction
24. Terminology Forward 1 Forward 2 Forward 3 Forward 4 Forward 5 Rollback 1 Rollback 2 Rollback 3 Rollback 4 Rollback 5
26. Implicit Assumptions and Requirements
27. Compensating Closures Cannot Abort
28. Idempotent Requests
29. What if?? Forward 1 Forward 2 Forward 3 Rollback 1 Rollback 2 Rollback 3 BOOM
30. What if?? Forward 1 Forward 2 Forward 3 Forward 4 Rollback 1 Rollback 2 Rollback 3
31. Futures in Erlang
32. Why does Erlang need futures?!
33. It doesn’t! Except…
34. Asynchronous Saga Operations
36. Implementation
37. Semantics?
38. Property Based Tests
39. What is it? §Write one or more invariants §Test values are automatically generated and the invariant tested §Failures are shrunk to the smallest possible failure case §Modify code (or test case) and restart test §Tests are usually timeboxed §Extremely useful to build confidence in complex scenarios
40. Academic history QuickCheck: A Lightweight Tool for Random Testing of Haskell Programs
41. Implementations for §Go §C/C++ §Clojure §Scala §Haskell (of course) §… lots of others … §Erlang/Elixir (watch Thomas Arts talk at ElixirConf EU 2015)
42. Erlang implementations §Quviq Commercial QuickCheck (http://www.quviq.com) §Free (but not open source) “QuickCheck mini” – doesn’t do statem §PropEr (https://github.com/manopapad/proper) §Triq (https://github.com/triqng/triq)
43. Generators §All standard basic types: §integers, §floats, §atoms, §binaries, §strings, §lists §Lists of basic types §User defined generators using ?LET and ?SUCHTHAT
44. Propositions §?FORALL(Variable, generator_function(), test_function(Variable))
45. Resources §https://github.com/mrallen1/gisla §https://github.com/mrallen1/criswell §Sagas paper: http://www.cs.cornell.edu/andru/cs711/2002fa/reading/sagas.pdf §Caitie McCaffrey, Papers We Love on Sagas: https://youtu.be/7dc4Tl5ZHRg?t=27m16s §Caitie McCaffrey, Distributed Sagas: https://speakerdeck.com/caitiem20/distributed-sagas-a-protocol-for- coordinating-microservices §These slides: https://speakerdeck.com/mrallen1/sagas-distributed-transactions- without-locks