Handle cache-update conflicts in distributed services

Q: Handle cache-update conflicts in distributed services

This question evaluates a candidate's competency in distributed systems and data consistency, focusing on cache–database consistency, concurrent write handling, versioning/CAS, distributed locking, cache invalidation strategies, idempotency, and failure recovery in high-throughput services.

Q: How do I approach System Design interview questions?

System Design questions require understanding of core concepts and practice. PracHub provides solutions with explanations to help you master system design interviews.

Q: What difficulty level is this interview question?

This is a hard difficulty System Design question, commonly asked during Onsite rounds at eBay.

Q: What role is this question designed for?

This question is commonly asked for Software Engineer candidates at eBay during technical interviews.

Question

Design: Cache–Database Consistency with Concurrent Writers

Context

You operate a high-throughput service using a cache (e.g., Redis) in front of a relational database. Multiple application servers may concurrently update the same logical record (key). You must prevent and resolve cache–database update conflicts and race conditions while keeping performance high.

Requirements

Design how to prevent and resolve conflicts across these areas:

Write ordering and atomicity
Versioning/ETags and compare-and-set (CAS)
Distributed locks (when and how)
TTLs and cache invalidation vs write-through/write-back
Idempotent updates and retries
Recovery after partial failures

Specify:

APIs (read/write), including headers or RPC fields
Data model (DB and cache)
Consistency guarantees
Trade-offs and when to choose each option

Provide read and write flows, including conflict resolution and failure handling.

Handle cache-update conflicts in distributed services

Quick Overview

Design: Cache–Database Consistency with Concurrent Writers

Context

Requirements

Solution

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