Database goldmines: internals without the folklore

Databases are the rare field where the best material is genuinely free and genuinely deep — and still most engineers never get past ORM folklore. This is the path through.

The one every backend engineer should have read

• Use The Index, Luke — Markus Winand. A free book-length site on exactly one thing: how SQL indexing actually works (B-trees, composite index column order, index-only scans, why LIKE '%x' can’t use an index) across Postgres, MySQL, Oracle, and SQL Server. The highest ratio of “queries fixed per page read” of anything on this site. His Modern SQL covers what SQL grew after 1992 — window functions, lateral joins, FILTER — that most people still write application code to avoid.

The courses that replaced the textbook

• CMU 15-445: Database Systems — Andy Pavlo. Every lecture on YouTube, every project public: build a buffer pool, a B+tree, query executors, and concurrency control inside a real storage manager (BusTub). This is the modern internals course.
• CMU 15-721: Advanced Database Systems — the graduate sequel: vectorized execution, query compilation, MVCC variants, modern OLAP architecture, taught through the papers that defined each.

The books

• Database Internals — Alex Petrov. The book for the layer the courses build: storage engines (B-trees in anger, LSM trees) in the first half, distributed consensus and replication in the second. Reads like a guided tour of the source code of every database you use.
• Readings in Database Systems (“the Red Book”) — Bailis, Hellerstein, Stonebraker. Free: the field’s judgment layer — which papers mattered and why, with Stonebraker’s opinions attached. Read it to acquire taste, not facts.
• Architecture of a Database System — Hellerstein, Stonebraker, Hamilton. An 80-page paper that is secretly the best systems-design document ever written: process models, admission control, and how the pieces of a DBMS fit.

Build-one-in-public blogs

• Phil Eaton — databases from scratch, in public: write-ahead logs, MVCC, io_uring, Raft — each post a working implementation plus honest notes. Also runs /r/databasedevelopment’s reading ecosystem-adjacent lists that are better curated than any official syllabus.
• build-your-own.org — James Smith’s free books: build a Redis, a database, a compiler, from empty file to working system in small verified steps. The database one is the fastest route from “read about B-trees” to “wrote one.”
• transactional.blog — Alex Miller (FoundationDB). The deepest public writing on transaction internals and distributed correctness testing — the “simulation testing” series explains the technique FoundationDB used to become the most trusted codebase in databases.
• Jamie Brandon — query languages and incremental computation; “Internal consistency in streaming systems” will change how you look at every streaming pipeline demo.

How to use this layer

Pick the pairing that matches your gap: queries slow → Winand this week; want internals → 15-445 projects with Petrov as the reference; designing systems → the Red Book and the Hellerstein paper. And one habit from all of them: EXPLAIN ANALYZE before believing anything — the planner is the territory, everything else is map.