Intermediate LevelSystem Design & Architecture
What is the Two-Phase Commit (2PC) protocol and why does it suffer from blocking risks?
❓ Interview Prompt: Explain Two-Phase Commit (2PC), Phase 1 (Prepare) vs Phase 2 (Commit/Abort), Coordinator node SPOF, and blocking lock risks.
The Two-Phase Commit (2PC) protocol coordinates atomic transactions across multiple distributed database nodes:
2 Phases:
1
Phase 1 (Prepare): Coordinator asks all participant nodes if they can commit. Participants acquire locks and vote 'YES' or 'NO'.
2
Phase 2 (Commit/Abort): If all vote 'YES', Coordinator commands all nodes to 'COMMIT'. If any vote 'NO', Coordinator commands 'ABORT'.
•
⚠️ Blocking Risk: If the Coordinator crashes during Phase 2, participant nodes remain indefinitely blocked holding database locks!
Code Implementation Example
markdown
Two-Phase Commit (2PC) Protocol Flow:
[Coordinator] ──(Phase 1: Prepare?)──> [Node A] [Node B]
[Coordinator] <-- (Vote: YES/YES) ─── [Node A] [Node B]
[Coordinator] ──(Phase 2: Commit!)──> [Node A] [Node B]💡Two-Phase Commit (2PC) Prepare and Commit phases.
🎯 Interview Key Takeaway
Avoid 2PC for high-throughput microservices due to coordinator blocking risks; prefer eventual consistency Saga patterns.
#System Design#2PC#Two-Phase Commit#Distributed Transactions#Intermediate
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