Rails 8 Solid Cache: Database-Backed Cache Store

Rails 8 introduces Solid Cache as the default production cache store, replacing Redis/Memcached with a database-backed solution that leverages modern SSD performance. The post covers installation for new and existing apps, configuration options (max_age, max_size, compression, sharding), real-world usage patterns (fragment caching, Russian doll caching, API response caching), and key tradeoffs including FIFO vs LRU eviction, 1–5ms latency vs Redis's 0.1–0.5ms, write amplification, lack of pub/sub support, and cold-start thundering herd issues. Guidance is provided on when to use Solid Cache versus sticking with Redis, plus performance tuning tips for compression, connection pooling, and migration steps.