The document discusses the Saga pattern, which involves breaking long-running transactions into multiple steps across services to maintain data consistency. A Saga is a collection of sub-transactions coordinated by a central orchestrator. If a step fails, compensation actions can rollback previous steps to return the system to a valid state. While complex, the Saga pattern allows for asynchronous and resilient transactions without tightly coupling services.

1. Saga Pattern
By Alexandr Prygun
Saga Pattern
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Saga pattern

4. Monolith App
Saga Pattern
API Application Database
One call One transactionIncoming call

5. Saga Patterm
API
Gateway
Application 1 Database 1
Application 2 Database 2
Application 3 Database 3
Incoming call
SOA/Microservices App

6. Saga Pattern
2PC: Prepare Phase
API
Gateway
Application 1 Database 1
Application 2 Database 2
Application 3 Database 3
Incoming call
Propose
Vote
Propose
Vote
Propose
Vote

7. Saga Pattern
2PC: Commit Phase
API
Gateway
Application 1 Database 1
Application 2 Database 2
Application 3 Database 3
Incoming call
Commit/Abort
Done
Commit/Abort
Done
Commit/Abort
Done

8. Saga Pattern
2PC: Disadvantages
- Data stays locked until commit or abort command
- There is no mechanism to rollback other transactions in case one service fails
- Others have to wait until the slowest resource finish its confirmation.
- Bad scaling

9. Saga Pattern
Sagas History
Long Live Transactions
Hector Garcia-Molina, Kenneth Salem,
Princeton University, 1987

10. Saga Pattern
What is Saga?
- Saga is long-lived transaction
- Saga is collection of sub-transactions

11. Saga Pattern
Saga orchestrator
Hotel
Booking
Service
Database 1
Rent Car
Service Database 2
Flight Tickets
Service Database 3
Book Trip Start saga
Start book hotel
End book hotel
Start book car
End book car
Start book tickets
End book tickets
End saga

12. Saga Pattern
Saga choreography
Hotel
Booking
Service
Database 1
Rent Car
Service Database 2
Flight Tickets
Service Database 3
Book Trip Start saga
Hotel is booked
Car is booked
End saga
Tickets are booked

13. Saga Pattern
Unsuccessful Saga
Start saga
1. Start book hotel
2. End book hotel
3. Start book car
4. End book car
5. Start book flights
6. Flights booking fail
Abort saga
7. Start cancel car
8. End cancel car
9. Start cancel hotel
10. End cancel hotel
End saga
Commit steps
Rollback steps

14. Saga Pattern
Saga pros and cons
Main advantage is that it helps maintain data consistency across
multiple services without tight coupling.
Main disadvantage is the complexity from a programming point
of view. Compensating transaction should be designed.

15. Saga Pattern
Saga tips
- A unique distributed transaction ID should be created for each saga and it
should be present in each related command or event
- Saga commands should be idempotent
- All components should implement compensate commands handlers
- Compensate commands should be idempotent as well
- Avoid synchronous operations

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