Caching

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Theory
Quiz

    Fundamentals

    • What is a cache, and what are the primary reasons for adding one to a system?

      Junior

    • What is the difference between a cache hit and a cache miss, and what do we mean by a 'cold' versus a 'warm' cache?

      Junior

    • What is the difference between memoization and caching?

      Junior

    • When is caching actually a bad idea? Can you name scenarios where adding a cache would decrease performance or reliability?

      Mid

    • How does the principle of temporal and spatial locality justify the use of a cache in the first place?

      Mid

    • Why might you choose NOT to cache a piece of data even if it is frequently accessed?

      Mid

    • Under what circumstances might adding a cache actually increase the overall latency of a request?

      Mid

    • What makes a good cache key? What pitfalls should you avoid when designing cache keys?

      Mid

    • What characteristics make a piece of data a good candidate for caching versus a poor one?

      Mid

    • What are virtual nodes in consistent hashing and what problem do they solve?

      Senior

    • Why is the choice of serialization format (JSON vs. Protobuf vs. Binary) important when designing a high-performance caching layer?

      Senior

    Caching Patterns

    • What is the fundamental difference between the Cache-Aside (Lazy Loading) pattern and the Read-Through pattern, and in which layer does the loading logic reside for each?

      Mid

    • Explain the trade-off between Write-Through and Write-Back (Write-Behind) caching. Which one would you choose for a system where data loss is unacceptable, and why?

      Mid

    • When would you use a Write-Around policy instead of Write-Through, and how does it impact the cache miss rate for subsequent reads?

      Mid

    • Compare Write-Through, Write-Back (Write-Behind), and Write-Around. What are the data loss risks associated with Write-Back?

      Mid

    • Explain the 'Dual Write' problem. How do you ensure the cache and database don't get out of sync during an update?

      Senior

    • Why might you prefer moving caching logic into a library or sidecar (Read-Through) rather than handling it manually in your application code?

      Senior

    • In a cache-aside pattern, on a write should you update the cache or delete (invalidate) the entry? Why is deleting often safer?

      Senior

    Eviction Policies

    • What happens to a cache when it reaches its memory limit but no TTLs have expired yet?

      Junior

    • Compare Least Recently Used (LRU) and Least Frequently Used (LFU). In what specific traffic pattern would LFU outperform LRU?

      Mid

    • How would you define and measure a 'Cache Hit Ratio'? What does a high hit ratio with high latency suggest about your cache design?

      Mid

    • Explain the trade-off between memory usage and hit ratio when sizing a cache.

      Mid

    • If your cache is primarily storing user session data that expires after 30 minutes of inactivity, which eviction policy would you configure and why?

      Mid

    • When would Most Recently Used (MRU) eviction outperform LRU?

      Mid

    • What is a 'healthy' cache hit ratio, and if your ratio is low, what specific architectural issues or traffic patterns would you investigate?

      Senior

    • Explain the concept of the 'Clock' or 'Second Chance' eviction policy. How does it approximate LRU with less overhead?

      Senior

    • What is the 'Belady's Anomaly' in the context of FIFO cache eviction?

      Senior

    • How does an ARC (Adaptive Replacement Cache) attempt to improve upon standard LRU?

      Senior

    • What is the 'Two-Segment' or 'LRU-K' algorithm, and why might it be better than standard LRU for certain workloads?

      Senior

    Http Caching

    • What happens to a cached resource when a 'Conditional GET' (If-None-Match) returns a 304 Not Modified?

      Junior

    • Explain the Cache-Control: no-cache vs. no-store directives. Which one allows the browser to keep a copy?

      Mid

    • What is the purpose of the Vary HTTP header in caching, and how does it prevent a mobile user from receiving a cached desktop version of a page?

      Mid

    • How do ETags work to facilitate conditional GET requests, and how does this save bandwidth?

      Mid

    • Explain the public vs. private directives in Cache-Control. Why is this distinction critical for security when caching authenticated responses?

      Mid

    • What is the difference between the ETag and Last-Modified headers?

      Mid

    • Explain the difference between freshness (Cache-Control/Expires) and validation (ETag/Last-Modified) in HTTP caching. When does a browser send a Conditional GET?

      Mid

    • What is the difference between 'Strong Validation' (ETags) and 'Weak Validation' in HTTP caching?

      Senior

    Ttl & Expiration

    • How does a sliding TTL differ from a fixed TTL?

      Junior

    • Explain the Stale-While-Revalidate pattern. How does it improve user-perceived latency while still ensuring data eventually becomes fresh?

      Mid

    • What is the purpose of cache warming or pre-warming, and when is it necessary to do this before a deployment or high-traffic event?

      Mid

    • What is the difference between evicting data based on a Time-To-Live (TTL) versus evicting based on memory pressure (Max-Memory), and can a key be evicted before its TTL expires?

      Mid

    • How do you determine the optimal TTL (Time-to-Live) for a specific piece of data?

      Mid

    • What is the difference between active (eager) expiration and lazy (passive) expiration of TTL'd entries, and what are the trade-offs?

      Mid

    • What is the difference between explicit (event-based) invalidation and time-based (TTL) expiration, and when would you combine them?

      Mid

    • What is 'Refresh-Ahead' caching, and how does it help in reducing tail latency?

      Senior

    Cache Failure Modes

    • What is Cache Penetration, how does it differ from a standard cache miss, and why is negative caching or a bloom filter used to solve it?

      Mid

    • Explain the Cache Avalanche scenario. How can jitter (adding randomness to TTLs) prevent a database from crashing during a mass expiration event?

      Mid

    • Explain the difference between 'Cache Penetration' and 'Cache Avalanche'. How do their mitigations differ?

      Mid

    • How does 'Negative Caching' help protect your downstream database?

      Mid

    • What is a Cache Stampede, and how does request coalescing or locking prevent multiple concurrent requests from recomputing the same expensive value?

      Senior

    • How do you identify and handle a hot key (a single key receiving disproportionately high traffic) in a distributed cache to prevent a single node from becoming a bottleneck?

      Senior

    • What is the difference between a cache avalanche and a cache stampede?

      Senior

    • How does a Bloom filter actually work, and why are false positives (but not false negatives) acceptable when using it to guard a cache?

      Senior

    Distributed Caching

    • What is the difference between an In-Process (Local) cache and a Distributed (Remote) cache? When would you choose one over the other?

      Junior

    • How does consistent hashing minimize cache misses when adding or removing a node from a distributed cache cluster?

      Mid

    • What is Consistent Hashing, and why is it preferred over simple 'mod N' hashing for distributing cache keys across a cluster?

      Mid

    • Explain the difference between sharding (partitioning) and replication in a cache cluster. Which one helps with read throughput, and which one helps with storage capacity?

      Mid

    • From a high-level architectural perspective, why might you choose Redis over Memcached (or vice-versa) for a caching layer?

      Mid

    • What is 'Multi-level Caching' (L1/L2 application caches), and how do you manage the complexity of multiple layers?

      Senior

    • What is 'Near Caching' and how does it leverage both local and distributed layers?

      Senior

    • In a distributed system, how do you ensure cache coherence across different geographical regions?

      Senior

    Invalidation & Consistency

    • What is the 'Cache Invalidation' problem, and why is it considered one of the 'two hard things' in computer science?

      Mid

    • How does using a versioned key (e.g., user:v2:123) help with cache invalidation during a schema change or deployment?

      Mid

    • What is the difference between Strong Consistency and Eventual Consistency in a multi-node cache cluster?

      Mid

    • Explain the concept of 'Eventual Consistency' in the context of a cache-aside pattern.

      Mid

    • Explain the 'Cache Coherence' problem when using local caches across multiple application instances.

      Senior

    • If your system requires strong consistency, can you still use a cache, and what are the trade-offs in latency if you do?

      Senior

    • How do you propagate cache invalidation across multiple distributed cache nodes or application instances (e.g., via pub/sub or broadcast messages)?

      Senior