Distributed Transaction Vocabulary

1. In two-phase commit (2PC), the node that initiates the transaction, sends prepare messages to all participants, and then issues the final commit or abort decision is called the:

Participant Coordinator Leader

2. A monitoring alert fires: 'The coordinator timed out waiting for a prepare response from the payments service.' What action must the coordinator take in 2PC when this happens?

Commit to the nodes that did respond Abort the entire transaction — a missing vote is treated as a no-vote Retry the prepare message indefinitely

3. An order service, an inventory service, and a payment service each have their own database. To ensure atomicity across services — either all steps succeed or all are undone — without using 2PC, the team uses a sequence of local transactions with compensating rollback steps for each. What pattern is this?

Distributed locking Saga pattern Two-phase commit

4. Each service in a saga receives an event, performs a local transaction, and publishes a success or failure event for the next step to consume. There is no central orchestrator. What saga coordination style is this?

Orchestration saga — a central coordinator tells each service what to do Choreography saga — services react to events from each other without a central controller Two-phase saga commit

5. A system design document states: 'We use the Saga pattern as an alternative to 2PC to achieve atomicity across services.' What is the key trade-off the team is accepting by choosing Saga over 2PC?

The Saga pattern provides stronger atomicity than 2PC The Saga pattern avoids distributed locks and coordinator blocking, but provides only eventual atomicity — intermediate states are visible to other services between saga steps The Saga pattern requires all services to share a single database

Vocabulary Reference

Term	Meaning
two-phase commit (2PC)	A distributed protocol with a prepare phase (all participants vote yes/no) and a commit phase (all commit or all abort). Provides strict atomicity but can block if the coordinator crashes.
coordinator	The node that drives 2PC: sends prepare, collects votes, issues the final commit or abort.
participant	A node that receives prepare from the coordinator, locks resources, votes yes or no, then awaits the commit/abort decision.
the coordinator timed out	A 2PC failure condition where the coordinator receives no prepare response from a participant; the coordinator must abort the transaction.
saga pattern	A sequence of local transactions across services, each with a compensating transaction that undoes its effect if a later step fails — an alternative to 2PC for atomicity across services.
atomicity across services	The guarantee that a multi-service operation either fully succeeds or is fully undone — achieved by 2PC (strict) or the Saga pattern (eventual).

Vocabulary Reference

Exercise complete!