Caching Beginner
Cache Eviction Lab
Predict cache hits and misses as requests flow through an LRU cache, then experiment with TTL behavior and stale data tradeoffs.
- Time
- 5-8 minutes
- Concept
- Cache hits, misses, LRU, TTL, and stale data
Backend concept
Caching
Cache hits, misses, LRU eviction, TTL, stale data, cache warming, and hit-rate thinking.
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Why this matters
Caches can make systems fast, but they also create freshness and invalidation tradeoffs.
How to practice
Predict hit/miss behavior and know when LRU or TTL changes the answer.
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Local review for this concept
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Learning objectives
- Predict cache hits and misses from a request sequence.
- Visualize LRU eviction as cache capacity fills.
- Understand how TTL changes freshness and hit rate.
- Map common API outcomes to precise HTTP status codes.
- Distinguish authentication, authorization, validation, and conflict responses.
- Recognize when success responses should include a body, a location, or no content.
Common mistakes to avoid
- Thinking cache capacity is unlimited.
- Forgetting that reading an item updates its recency in LRU.
- Using long TTLs for data that must be fresh.
- Returning 200 OK for every API response and hiding errors inside the JSON body.
- Using 404 Not Found for authorization failures that should be 403 Forbidden.
- Using 500 Internal Server Error for client validation mistakes.
Games for Caching
Start with the first game, then use local review history to revisit missed decisions.
APIs Beginner
HTTP Status Defender
Choose the correct HTTP status code for realistic backend scenarios and learn the response semantics behind each answer.
- Time
- 5-8 minutes
- Concept
- HTTP status codes and response semantics
Scaling Intermediate
Rate Limit Architect
Choose rate limiting designs for realistic backend traffic patterns, from public APIs and login endpoints to queues, webhooks, and retry storms.
- Time
- 6-9 minutes
- Concept
- Rate limiting, fairness, backpressure, and abuse protection