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A measured tour of B-tree indexes on PostgreSQL 17, with real query plans for index-only scans, the visibility map, HOT updates, and the selectivity point where the planner abandons your index.

You have a UserService that needs a Database. Your OrderService needs UserService, Database, and a PaymentGateway. Your NotificationService needs EmailClient and UserService.

You've probably seen gRPC described as "REST but faster." That framing is technically true and practically useless.

"Our database is highly available" means four different things, and they protect against four different failures. A ladder for forcing that conversation to be specific — plus why the money most teams spend on availability goes to the failure modes they face least.

EJS, Handlebars, Pug and Nunjucks all do the same three things: tokenize, parse, compile. Build a real one — loops, conditionals, partials, escaping by default — and see exactly where HTML escaping stops protecting you.

You've run git commit thousands of times. But have you ever wondered what actually happens when you do? Git isn't a file-syncing tool with version numbers bolted on.

Kafka is a distributed commit log, not a message queue. Segments on disk, the ISR, the KRaft controller quorum and zero-copy fetches — and how each one explains a config option you've had to set.

Here's a scenario I see in almost every codebase I review. A developer writes an async function that reads some state, does a bit of work, then writes back a result. In tests, it's fine. In development, it's fine.

A client-side router watches the URL, matches it against patterns, and calls a handler. Build one in 110 lines — params, wildcards, back/forward — and see the four decisions every router makes for you.