Explain caching strategies and common failure modes.
Interviewer Expectations for this Question
01
Core Competency
Assesses fundamental understanding of System Design conventions, runtime behavior, and memory/performance considerations.
02
Evaluation Criteria
Hiring managers look for precision, avoidance of ambiguous jargon, and ability to explain trade-offs under real production conditions.
Comprehensive Model Answer
Verified Solution
Strategies:
- Cache-aside (lazy loading): app checks cache, on miss reads DB and populates. Most common.
- Read-through: cache library fetches on miss.
- Write-through: write to cache and DB together for consistency.
- Write-behind: write to cache, flush to DB asynchronously for throughput with some durability risk.
Eviction: LRU/LFU/TTL. Place caches at multiple layers: client, CDN, application (Redis/Memcached), and database.
Failure modes:
- Stampede/thundering herd: many requests miss the same key; use locks, single-flight or jittered TTLs.
- Cache penetration: repeated misses for non-existent keys; cache negatives or use a bloom filter.
- Stale data: invalidation is hard; set TTLs, publish invalidation events, or version keys.
- Hot key overload: shard or replicate the key.
Candidate Response Strategy & Interview Tips
- Start with a concise one-sentence summary: Deliver a direct, confident answer first before expanding into nuances.
- Demonstrate real-world trade-offs: Discuss where this approach excels and when you would avoid it in production systems.
- Discuss complexity & edge cases: Proactively explain time/space complexity or boundary conditions (null values, scale limits).
- Prepare for interviewer follow-ups: Technical hiring panels frequently probe deeper into concurrency, backward compatibility, or alternative libraries.