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hardSystem Design

What is the saga pattern for distributed transactions?

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01

Understand the problem

Explain sagas.

sagatransactions
02

Attempt it yourself

Sketch your approach before reading the solution — that's what interviews test.

Nudge consolestandby

Stuck? Beam a request up — the console returns a conceptual nudge that guides your logic without spoiling the implementation.

03

Study the solution

Step 1: Outline use cases and constraints

Gather requirements and scope the problem. Ask questions to clarify use cases and constraints. Discuss assumptions.

Use cases

We'll scope the problem to handle only the following use cases

  • User needs to understand saga to make architecture decisions

Solution ready — 2 min read

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04

Read the code

Orchestrated saga with compensations
Run Playground
def create_order():  print("  create order");  return True
def charge_card():   print("  charge card");    return True
def reserve_stock(): print("  reserve stock");  return False   # fails

def cancel_order():  print("  compensate: cancel order")
def refund_card():   print("  compensate: refund card")

# (action, compensation) pairs run in order; undo completed steps on failure.
steps = [
    (create_order, cancel_order),
    (charge_card,  refund_card),
    (reserve_stock, lambda: None),
]

done, ok = [], True
for action, compensate in steps:
    if action():
        done.append(compensate)
    else:
        ok = False
        print("step failed -> compensating", len(done), "completed step(s)")
        for c in reversed(done):       # reverse order
            c()
        break

print("saga", "committed" if ok else "rolled back")
05

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