Distributed Transactions (Saga vs 2PC)

Question 1

In the Saga pattern, how do you handle a failure in the final step of a transaction?

Accepted Answer

Compensating transactions — The Saga pattern issues Compensating Transactions (like a refund event) backwards down the chain to undo previously successful steps.

Question 2

A distributed transaction must maintain atomicity across…

Accepted Answer

Multiple services — It coordinates operations spanning several independent systems so they succeed or fail as a unit — much harder than a single-DB transaction.

Question 3

Two-Phase Commit (2PC) has which two phases?

Accepted Answer

Prepare and Commit — In phase 1 the coordinator asks all participants to prepare/vote; in phase 2 it tells them to commit only if all voted yes.

Question 4

The COORDINATOR in 2PC is responsible for…

Accepted Answer

Collecting votes to decide — It orchestrates the global decision; participants follow its commit/abort instruction after voting.

Question 5

A major weakness of 2PC is that it is…

Accepted Answer

Blocking on coordinator failure — Participants that voted 'yes' must wait for the coordinator's decision; its failure can block them indefinitely, holding resources/locks.

Question 6

The SAGA pattern handles distributed transactions by…

Accepted Answer

A sequence of compensable steps — Each step commits locally; if a later step fails, previously completed steps are reversed via compensating transactions (semantic rollback).

Question 7

A 'compensating transaction' in a Saga…

Accepted Answer

Undoes a prior step — Since there's no global rollback, each step defines an inverse action to compensate if the overall saga must abort.

Question 8

Sagas typically provide ___ consistency rather than strong consistency.

Accepted Answer

Eventual consistency — During a saga, intermediate states are visible; the system reaches consistency once all steps (or compensations) complete.

Question 9

Saga ORCHESTRATION uses…

Accepted Answer

A central orchestrator — Orchestration centralizes the saga's control flow in one coordinator; CHOREOGRAPHY instead has services react to each other's events.

Question 10

Saga CHOREOGRAPHY coordinates steps via…

Accepted Answer

Services reacting to events — Each service listens for events and triggers the next action, giving loose coupling but making the overall flow harder to track.

2PC or saga?

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In the Saga pattern, how do you handle a failure in the final step of a transaction?

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