NoSQL & Polyglot Persistence covers: NoSQL Distilled, Redis 4.x Cookbook, MongoDB — The Definitive Guide. Understand when and why to use non-relational databases alongside PostgreSQL. Master Redis (you already use it) and MongoDB (you should understand it), and develop a framework for choosing the right database for each use case.
When to use Redis: caching (Rails.cache with redis_cache_store), sessions (session_store :redis_store), background jobs (Sidekiq), real-time features (Action Cable pub/sub), rate limiting. When to stay on PostgreSQL: everything else. Why most Rails apps do not need MongoDB: PostgreSQL's JSONB gives you document-style flexibility with relational guarantees. You can jsonb_path_query, GIN-index JSONB fields, and still JOIN with relational tables. The Turbo/Hotwire stack uses Redis for Action Cable pub/sub. Understanding Redis data structures (not just "it's a cache") lets you build features that would be painful with only PostgreSQL: leaderboards with ZRANGEBYSCORE, rate limiting with INCR + EXPIRE, unique visitor counting with PFADD (HyperLogLog).
This course unlocks once you've finished its prerequisite. Open prerequisite →
Hot take: most Rails apps do not need MongoDB. They do not need DynamoDB either. PostgreSQL with JSONB covers ninety-five percent of "flexible schema" use cases that people reach …
Sooner or later the meeting happens. A model has grown a pile of variable attributes — custom fields, per-tenant settings, a metadata column nobody planned — and someone proposes …
Right now, in production, your application depends on Redis in at least three places — Rails.cache, Sidekiq's queues, Action Cable's pub/sub — and here is the uncomfortable questi…
You may never run MongoDB in production. Read this book anyway, for the same reason a defense lawyer studies the prosecution: the document-store proposal will cross your desk even…
Work through each item before the checkpoint.
The five Redis patterns every Rails app eventually needs, built against a real Redis: a sliding-window rate limiter, a sorted-set leaderboard, real-time counters, a session store …
6 lessons. Read in order; spiral back when you need to. By the end you'll have used the core ideas twice — once on the abstract, once on something you'll meet at work next week.