Applying the Saga Pattern

Applying the Saga Pattern

As we build larger more complex applications and solutions that need to do collaborative processing the traditional ACID transaction model using coordinated 2-phase commit is often no longer suitable. More frequently we have long lived transactions or must act upon resources distributed across various locations and trust boundaries. The Saga Pattern is a useful model for long lived activities and distributed transactions without coordination.

Sagas split work into a set of transactions whose effects can be reversed even after the work has been performed or committed. If a failure occurs compensating transactions are performed to rollback the work. So at its core the Saga is a failure Management Pattern, making it particularly applicable to distributed systems.

In this talk, I'll discuss the fundamentals of the Saga Pattern, and how it can be applied to your systems. In addition we'll discuss how the Halo 4 Services successfully made use of the Saga Pattern when processing game statistics, and how we implemented it in production.

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Caitie McCaffrey

May 12, 2015
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Transcript

  1. 3.
  2. 13.

    –Corbett et al. “Spanner is Google’s scalable, multi-version, globally distributed,

    and synchronously- replicated database. It is the first system to distribute data at global scale and support externally-consistent distributed transactions.”
  3. 14.

    “The key enabler of these properties is a new TrueTime

    API and its implementation…using multiple modern clock references (GPS and atomic clocks).” –Corbett et al.
  4. 21.

    “A Saga is a Long Lived Transaction that can be

    written as a sequence of transactions that can be interleaved. All transactions in the sequence complete successfully or compensating transactions are ran to amend a partial execution.”
  5. 25.

    Saga Guarantee Either • T1, T2 … Tn or •

    T1, T2 … Tj, Cj, … C2, C1
  6. 29.

    • Book Hotel (T1 ) • Book Car (T2 )

    • Book Flight (T3 ) • Cancel Hotel (C1 ) • Cancel Car (C2 ) • Cancel Flight (C3 ) Sagas
  7. 31.

    Saga Log • Begin Saga • End Saga • Abort

    Saga • Begin Ti • End Ti • Begin Ci • End Ci
  8. 32.

    Begin Saga! Start Book Hotel (T1 ) End Book Hotel

    (T1 ) Start Book Car Rental (T2 ) End Book Car Rental (T2 ) Start Book Flight (T3 ) End Book Flight (T3 ) End Saga Successful Saga
  9. 33.

    Begin Saga Start Book Hotel (T1 )! End Book Hotel

    (T1 ) Start Book Car Rental (T2 ) End Book Car Rental (T2 ) Start Book Flight (T3 ) End Book Flight (T3 ) End Saga Successful Saga
  10. 34.

    Begin Saga Start Book Hotel (T1 ) End Book Hotel

    (T1 )! Start Book Car Rental (T2 ) End Book Car Rental (T2 ) Start Book Flight (T3 ) End Book Flight (T3 ) End Saga Successful Saga
  11. 35.

    Begin Saga Start Book Hotel (T1 ) End Book Hotel

    (T1 ) Start Book Car Rental (T2 )! End Book Car Rental (T2 ) Start Book Flight (T3 ) End Book Flight (T3 ) End Saga Successful Saga
  12. 36.

    Begin Saga Start Book Hotel (T1 ) End Book Hotel

    (T1 ) Start Book Car Rental (T2 ) End Book Car Rental (T2 )! Start Book Flight (T3 ) End Book Flight (T3 ) End Saga Successful Saga
  13. 37.

    Begin Saga Start Book Hotel (T1 ) End Book Hotel

    (T1 ) Start Book Car Rental (T2 ) End Book Car Rental (T2 ) Start Book Flight (T3 )! End Book Flight (T3 ) End Saga Successful Saga
  14. 38.

    Begin Saga Start Book Hotel (T1 ) End Book Hotel

    (T1 ) Start Book Car Rental (T2 ) End Book Car Rental (T2 ) Start Book Flight (T3 ) End Book Flight (T3 )! End Saga Successful Saga
  15. 39.

    Begin Saga Start Book Hotel (T1 ) End Book Hotel

    (T1 ) Start Book Car Rental (T2 ) End Book Car Rental (T2 ) Start Book Flight (T3 ) End Book Flight (T3 ) End Saga Successful Saga
  16. 41.

    Begin Saga! Start Book Hotel (T1 ) End Book Hotel

    (T1 ) Start Book Car Rental (T2 ) Abort Saga Start Compensate Car Rental (C2 ) End Compensate Car Rental (C2 ) Start Compensate Book Hotel (C1 ) End Compensate Book Hotel (C1 ) End Saga Unsuccessful Saga
  17. 42.

    Begin Saga Start Book Hotel (T1 )! End Book Hotel

    (T1 ) Start Book Car Rental (T2 ) Abort Saga Start Compensate Car Rental (C2 ) End Compensate Car Rental (C2 ) Start Compensate Book Hotel (C1 ) End Compensate Book Hotel (C1 ) End Saga Unsuccessful Saga
  18. 43.

    Begin Saga Start Book Hotel (T1 ) End Book Hotel

    (T1 )! Start Book Car Rental (T2 ) Abort Saga Start Compensate Car Rental (C2 ) End Compensate Car Rental (C2 ) Start Compensate Book Hotel (C1 ) End Compensate Book Hotel (C1 ) End Saga Unsuccessful Saga
  19. 44.

    Begin Saga Start Book Hotel (T1 ) End Book Hotel

    (T1 ) Start Book Car Rental (T2 )! Abort Saga Start Compensate Car Rental (C2 ) End Compensate Car Rental (C2 ) Start Compensate Book Hotel (C1 ) End Compensate Book Hotel (C1 ) End Saga Unsuccessful Saga
  20. 45.

    Begin Saga Start Book Hotel (T1 ) End Book Hotel

    (T1 ) Start Book Car Rental (T2 ) Abort Saga! Start Compensate Car Rental (C2 ) End Compensate Car Rental (C2 ) Start Compensate Book Hotel (C1 ) End Compensate Book Hotel (C1 ) End Saga Unsuccessful Saga
  21. 46.

    Begin Saga Start Book Hotel (T1 ) End Book Hotel

    (T1 ) Start Book Car Rental (T2 ) Abort Saga Start Compensate Car Rental (C2 )! End Compensate Car Rental (C2 ) Start Compensate Book Hotel (C1 ) End Compensate Book Hotel (C1 ) End Saga Unsuccessful Saga
  22. 47.

    Begin Saga Start Book Hotel (T1 ) End Book Hotel

    (T1 ) Start Book Car Rental (T2 ) Abort Saga Start Compensate Car Rental (C2 ) End Compensate Car Rental (C2 )! Start Compensate Book Hotel (C1 ) End Compensate Book Hotel (C1 ) End Saga Unsuccessful Saga
  23. 48.

    Begin Saga Start Book Hotel (T1 ) End Book Hotel

    (T1 ) Start Book Car Rental (T2 ) Abort Saga Start Compensate Car Rental (C2 ) End Compensate Car Rental (C2 ) Start Compensate Book Hotel (C1 )! End Compensate Book Hotel (C1 ) End Saga Unsuccessful Saga
  24. 49.

    Begin Saga Start Book Hotel (T1 ) End Book Hotel

    (T1 ) Start Book Car Rental (T2 ) Abort Saga Start Compensate Car Rental (C2 ) End Compensate Car Rental (C2 ) Start Compensate Book Hotel (C1 ) End Compensate Book Hotel (C1 )! End Saga Unsuccessful Saga
  25. 50.

    Begin Saga Start Book Hotel (T1 ) End Book Hotel

    (T1 ) Start Book Car Rental (T2 ) Abort Saga Start Compensate Car Rental (C2 ) End Compensate Car Rental (C2 ) Start Compensate Book Hotel (C1 ) End Compensate Book Hotel (C1 ) End Saga Unsuccessful Saga
  26. 51.

    –Molina et. al “Due to space limitations, we only discuss

    Sagas in a centralized System, although clearly they can be implemented in a distributed database system.” Sagas in Distributed Systems
  27. 53.

    \ • Book Hotel (T1 ) • Book Car (T2

    ) • Book Flight (T3 ) • Cancel Hotel (C1 ) • Cancel Car (C2 ) • Cancel Flight (C3 ) Requests instead of Transactions
  28. 54.

    A Distributed Saga is a Collection of Sub-Requests Each Sub-Request

    has a Compensating Request T1, T2 … Tn C1, C2 … Cn
  29. 55.

    Begin Saga Start Book Hotel Request (T1 ) End Book

    Hotel Request (T1 ) Start Book Car Rental Request (T2 ) End Book Car Rental Request (T2 ) Start Book Flight Request (T3 ) End Book Flight Request (T3 ) End Saga Successful Distributed Saga
  30. 57.

    Saga Execution Coordinator (SEC) • Interprets & Writes to Saga

    Log • Applies Saga Sub-Requests • Applies Saga Compensating Requests when Necessary
  31. 58.
  32. 59.
  33. 60.
  34. 61.
  35. 62.
  36. 63.
  37. 64.
  38. 65.
  39. 66.
  40. 68.
  41. 69.
  42. 70.
  43. 74.

    Safe States • All Executed Sub-Requests are Complete (Start Ti

    & End Ti both logged) • Saga has been Aborted, Proceed with Compensating Transactions
  44. 75.

    Un-Safe State • Start Ti logged, no End Ti logged

    Abort Saga Start Compensating Requests
  45. 76.
  46. 77.

    Distributed Saga Guarantee Either • T1, T2 … Tn or

    • T1, T2 … Tj, Cj, … C2, C1
  47. 79.
  48. 84.

    Store Stats Player One Store Stats Player Two Store Stats

    Player Three Store Stats Player Four Game Grain / SEC
  49. 86.

    Store Stats Player One Store Stats Player Two Store Stats

    Player Three Store Stats Player Four Game Grain / SEC
  50. 87.

    Store Stats Player One Store Stats Player Two Store Stats

    Player Three Store Stats Player Four Game Grain / SEC
  51. 88.

    Sagas • Long Lived / Distributed Transactions • Trade Atomicity

    for Availability • Failure Management Pattern