Lesson 5 / 32
Caching
Cut latency and database load with layered caching, cache-aside and write-through patterns, TTLs and eviction policies.
Where caches live
Browser, CDN, reverse proxy, application memory, and a shared store like Redis. Each layer absorbs reads so the database sees only the misses.
Write strategies
Cache-aside: app loads on miss, writes DB and invalidates. Write-through: write cache + DB together. Write-back: write cache now, DB later (fast, risky).
Always set a TTL
An expiry bounds staleness and stops a poisoned entry living forever. Add jitter to TTLs so keys don't all expire at once (thundering herd).
Quick check: Which eviction policy removes the entry unused for the longest time?
- FIFO
- Random
- MRU (most recently used)
- LRU
Answer
LRU — LRU (Least Recently Used) evicts the coldest entry by last access time.