ACID transactions don't work across services. You can't lock a row in Service A while updating Service B.
Sagas break transactions into steps. Each step has a compensating action. If step fails, run compensations for steps and .
Example: Order saga. : Reserve inventory. : Charge payment. : Ship order. If shipping fails, refund payment and release inventory.
Implementations: Choreography (events trigger next steps) or Orchestration (central coordinator).