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E-VAN - Sagas
- 1. What’s this “Saga” thing that everyone is talking about? @andreasohlund http://andreasohlund.net
- 2. What is a long running process? “A long running process is a process whose execution lifetime exceeds the time to process a single external event or message” - Udi Dahan
- 3. Long running process Step Step Start Start End Step Step Step
- 4. Long running process Step Step Start Start End Step Step Step
- 5. The problem • Holding locks for the duration of a long running transaction are more likely • To be deadlocked • To experience infrastructure failures
- 6. Long Lived Transactions Business Transaction Step Step Start End Step Step Step
- 7. Long Lived Transactions Business Transaction Step ACID ACID Step Start End ACID Step ACID Step ACID Step
- 8. The anatomy of a step Step
- 9. The anatomy of a step Step
- 10. The anatomy of a step Step Get current state Store
- 11. The anatomy of a step Step Get current state Store
- 12. Sagas vs Aggregate roots Event Command Saga Command Event AR
- 13. Sagas and bounded contexts Ext ern al E ven t Saga Command Event AR Bounded context
- 14. The birth of a saga Saga message Bus
- 15. The birth of a saga Create Saga Saga message instance Bus
- 16. The birth of a saga Create Dispatch Saga Saga message instance Bus
- 17. The birth of a saga Create Dispatch Saga Saga message instance Bus Send
- 18. The birth of a saga Create Dispatch Saga Saga message instance Bus Send Saga Save Persister
- 19. The birth of a saga Create Dispatch Saga Saga message instance Bus Send Saga Save Persister Store DB
- 20. Existing sagas Message Bus
- 21. Existing sagas Get Message Saga Bus Persister Load/Store DB
- 22. Existing sagas Get Message State Saga Saga Bus instance Persister Load/Store DB
- 23. Existing sagas Get Message State Dispatch Saga Saga Bus instance Persister Load/Store DB
- 24. Existing sagas Get Message State Dispatch Saga Saga Bus instance Persister Send Load/Store DB
- 25. Existing sagas Get Message State Dispatch Saga Saga Bus instance Persister Send Save Load/Store DB
- 26. State • Remember what steps have been executed • Gets persisted between each step • Temporary storage of data • Serialize access to the same saga instance • Unique index • Locking
- 27. Time • Long running transactions • Time is a business requirement • Needs to be durable and managed externally
Notes de l'éditeur
- LLT - Long lived transactions - Hector Garcia-Molina 87 Top level is a business transaction Does not comply to ACID Requires compensating actionsSecond level is acid compliantAnalyze the business to find the boundaries Add messages -> in order to make each step as short as possible + forward movement only
- Developers tends to do the same mistakes today
- Top level is a business transaction Does not comply to ACID Requires compensating actionsSecond level is acid compliantAnalyze the business to find the boundaries Add messages -> in order to make each step as short as possible + forward movement only
- One way messaging only to keep transaction as short as possible More scalable and robust http://www.udidahan.com/2008/06/23/sagas-solve-stupid-transaction-timeouts/ Can execute “steps” in parallelSaga instances are not run in parallelUse locks in DB to ensure that
- Not a hard rule Sagas are useful for other non DDD related things
- Sagas operate within a BC Can react to events from other BC’s
- Saga message handlers have state