Handle cache-update conflicts in distributed services

Q: Handle cache-update conflicts in distributed services

This is a System Design interview question from eBay for Software Engineer roles. View the full question and solution on PracHub.

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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

Design: Cache–Database Consistency with Concurrent Writers

Context

Requirements

Solution (Locked)

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