Concept Guides
Databases
Where applications keep their data, and how to model, query and scale it.
SQL vs NoSQL
Fixed, related tables enforced by a schema, versus document, key-value, and other stores that trade structure for flexibility or scale.
PostgreSQL
An open-source relational database known for strict standards compliance and a feature set that goes well beyond plain tables.
MySQL
The relational database that popularized SQL for the open-source web, and still one of the most widely deployed.
MongoDB
A document database that stores JSON-like records instead of rows, and lets each document's shape vary.
Redis
An in-memory key-value store used as a cache, a session store, and a lightweight message broker.
ORM Concepts
A layer that lets application code work with objects instead of writing SQL by hand, and the trade-offs that come with it.
Caching Strategies
Where to store a copy of data you've already fetched or computed, so the next request doesn't pay the same cost again.
Message Queues
A buffer that lets one part of a system hand off work to another without both needing to be online and fast at the same moment.