Redis labs
Redis is simple to start and subtle to use well. These labs run Redis commands in your browser to show each data structure, and simulate a cache in front of a database to reveal how eviction, TTLs and traffic patterns change your hit ratio.
2 free interactive labs — Redis Commands & Data Structures, Redis Caching: Cache-Aside, TTL & Eviction. Each one has an easy-to-hard set of examples, a written explanation and a FAQ, and runs entirely in your browser.
Strings, lists, hashes, sets and sorted sets, one command at a time.
Hit or miss? Watch LRU, LFU, TTLs and a cache stampede decide your database load.