Design a distributed transactions protocol to coordinate updates across multiple services or databases. Compare two-phase commit, three-phase commit, and Saga patterns; specify message flows, failure handling, idempotency, timeouts, and exactly-once versus at-least-once guarantees.

This question evaluates a candidate's understanding of distributed transactions, coordination protocols, fault tolerance, consistency, and reliability across microservices and databases.

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Design distributed transactions protocol | Google Interview Question

System Design: Distributed Transactions Across Multiple Services

Context

You must design a distributed transactions protocol to coordinate updates across multiple services or databases in a microservices environment. The network is unreliable (messages can be delayed, duplicated, or lost), services can crash and recover, and latency and availability matter.

Assume services communicate over RPC and/or a message bus. Some services may support a "prepare/commit" primitive; others may not.

Task

Propose a protocol to coordinate multi-service updates.
Compare and contrast the following approaches:
- Two-Phase Commit (2PC)
- Three-Phase Commit (3PC)
- Saga (orchestration and/or choreography)
For each approach, specify:
- Message flow (step-by-step)
- Failure handling (coordinator crash, participant crash, message loss/duplication, partition)
- Idempotency mechanisms
- Timeouts and retries
- Delivery guarantees (exactly-once vs at-least-once) and what you can realistically achieve
Conclude with a recommendation for when to use each approach and how to implement it safely.

Context

Assume services communicate over RPC and/or a message bus. Some services may support a "prepare/commit" primitive; others may not.

Task

Propose a protocol to coordinate multi-service updates.

Compare and contrast the following approaches:

Two-Phase Commit (2PC)
Three-Phase Commit (3PC)
Saga (orchestration and/or choreography)

For each approach, specify:

Message flow (step-by-step)
Failure handling (coordinator crash, participant crash, message loss/duplication, partition)
Idempotency mechanisms
Timeouts and retries
Delivery guarantees (exactly-once vs at-least-once) and what you can realistically achieve

Conclude with a recommendation for when to use each approach and how to implement it safely.

Design distributed transactions protocol

Quick Overview

System Design: Distributed Transactions Across Multiple Services

Context

Task

Solution

Submit Your Answer to Earn 20XP

Design distributed transactions protocol

Quick Overview

System Design: Distributed Transactions Across Multiple Services

Context

Task

Solution

Submit Your Answer to Earn 20XP