SQLite keeps data safe by wrapping every operation in a transaction, guaranteeing ACID properties. The article walks through how the engine uses transactions, file locking, and page‑level journaling to recover from crashes and maintain consistency, all while staying inside a single library.

By default, SQLite runs in autocommit mode, automatically wrapping each SQL statement in a system transaction. SELECT statements execute inside read‑transactions and never modify pages, while non‑SELECT commands start read‑transactions and upgrade to write‑transactions when they touch data, committing or aborting at the end.

Non‑SELECT commands hold a mutex for their entire run, ensuring statement‑level atomicity and clean rollbacks via the statement journal. In contrast, SELECT queries acquire and release the mutex between rows, allowing multiple readers to interleave while writers pause, preserving isolation without MVCC.

This lightweight design lets SQLite stay in a single library yet support concurrent access across processes through file locks and page‑level isolation. The article links to FreeDevTools, an open‑source hub for dev tools, and to the author’s GitHub experiments, inviting readers to explore the engine’s internals.