Distributed Transactions — Simple

Problem statement (interviewer prompt)

Design a multi-step transaction that spans three independent services (payment, inventory, shipping) where any step may fail. Explain how you'd implement it via 2PC vs TCC vs orchestrated saga vs outbox-pattern events, and which you'd actually pick in production.

flowchart LR
  ORC([Orchestrator])
  A[Service A<br/>charge card]
  B[Service B<br/>reserve item]
  C[Service C<br/>create order]
  CA[Compensate A<br/>refund]
  CB[Compensate B<br/>release]
  ORC --> A --> B --> C
  C -. on failure .-> CB -. on failure .-> CA

    classDef client fill:#dbeafe,stroke:#1e40af,stroke-width:1px,color:#0f172a;
    classDef edge fill:#cffafe,stroke:#0e7490,stroke-width:1px,color:#0f172a;
    classDef service fill:#fef3c7,stroke:#92400e,stroke-width:1px,color:#0f172a;
    classDef datastore fill:#fee2e2,stroke:#991b1b,stroke-width:1px,color:#0f172a;
    classDef cache fill:#fed7aa,stroke:#9a3412,stroke-width:1px,color:#0f172a;
    classDef queue fill:#ede9fe,stroke:#5b21b6,stroke-width:1px,color:#0f172a;
    classDef compute fill:#d1fae5,stroke:#065f46,stroke-width:1px,color:#0f172a;
    classDef storage fill:#e5e7eb,stroke:#374151,stroke-width:1px,color:#0f172a;
    classDef external fill:#fce7f3,stroke:#9d174d,stroke-width:1px,color:#0f172a;
    classDef obs fill:#f3e8ff,stroke:#6b21a8,stroke-width:1px,color:#0f172a;
    class A,B,C,CA,CB service;
    class ORC compute;

A saga = a sequence of local txs + matching compensations. 2PC = all-or-nothing across resource managers.