2.5 Distributed Transaction Solution: Saga

1. What Is Saga?

A distributed transaction solution that guarantees eventual consistency.

2. Saga Process

• There are multiple transaction participants, and each participant has two pieces of logic: a forward operation and a reverse operation.
• Divide the transaction into two phases:
  • In the first phase, each participant executes the forward operation.
  • The second phase depends on the result of the first phase.
    • If all forward operations execute successfully, the distributed transaction commits.
    • If any forward operation fails, go back and execute the reverse operations of the preceding participants.
• 

3. TCC vs Saga

• Similarities:
  • Both have two phases.
  • Both need to implement compensation operations.
• Differences:
  • TCC is synchronous, while Saga is asynchronous (event-driven).
  • TCC needs to reserve resources in the first phase, while Saga does not.

4. Use Cases for Saga

• Multiple services use multiple data sources, and each data source can be different.
• Participants include other companies or legacy-system services that cannot provide the three interfaces required by the TCC model.
• Business processes are long and have many steps.

5. Problems with Saga

Does not guarantee isolation.

6. Saga Implementation

6.1. Seata Saga Mode

7. References

• Seata Saga Mode
• Saga distributed transactions - Azure Design Patterns | Microsoft Docs
• A Brief Discussion of Saga Distributed Transactions - SegmentFault