File Locking And Concurrency In SQLite Version 3

This document was originally created in early 2004 when SQLite version 2 was still in widespread use and was written to introduce the new concepts of SQLite version 3 to readers who were already familiar with SQLite version 2. But these days, most readers of this document have probably never seen SQLite version 2 and are only familiar with SQLite version 3. Nevertheless, this document continues to serve as an authoritative reference to how database file locking works in SQLite version 3.

The document only describes locking for the older rollback-mode transaction mechanism. Locking for the newer write-ahead log or WAL mode is described separately.