Design a high-performance caching layer for a social media platform

0-2 years experience

1. 1How would you add a cache for user‑profile lookups to reduce database load in a small feature?
2. 2If a cached profile entry expires while a user is scrolling, what does the user see and how does your system handle it?

2-5 years experience

1. 1We saw latency spikes after a post went viral; how would you debug the caching layer to find the bottleneck?
2. 2Explain the trade‑offs between write‑through and write‑behind caching for new posts on the timeline.
3. 3Given a limited cache size, how would you decide which keys to evict and why?

5-8 years experience

1. 1Design the caching architecture to serve timeline reads for millions of users, covering sharding, replication, and cache invalidation.
2. 2How would you ensure cache consistency when a user changes their privacy settings that affect what appears in others' feeds?
3. 3What key metrics would you monitor and how would you auto‑scale the cache tier under load?

8+ years experience

1. 1Our platform is migrating from a monolithic cache to a multi‑region, edge‑distributed cache; what migration steps and data‑ownership concerns would you address?
2. 2How would you evaluate the cost‑benefit of adding a CDN‑level cache versus an in‑memory cache for serving media assets?
3. 3Describe a strategy to keep cache logic maintainable across multiple teams and services over several years.