Write-Ahead Log Explained: Build Crash-Safe Durability in 30 Lines

Excellent explanation of write-ahead logging. I especially liked how the article builds the concept from a simple in-memory Map, then introduces each improvement only after showing the exact failure it solves. The distinction between surviving a process crash and surviving a full power loss was particularly valuable, because write() versus fsync() is often oversimplified. The section on torn records and replay also made crash recovery feel practical rather than mysterious. Connecting the small implementation to PostgreSQL, SQLite, and LevelDB was a strong finish. This is a great example of teaching complex database internals through clear reasoning and experimentation.

I like how this derives the WAL from first principles rather than introducing it as a database feature. Once you frame everything around durability guarantees, concepts like append-only logs, replay, and fsync start feeling inevitable rather than magical.