SQLite's File Format

Summary

Database File Format Table Of Contents This document describes and defines the on-disk database file format used by all releases of SQLite since version 3.0.0 (2004-06-18). 1. The Database File The complete state of an SQLite database is usually contained in a single file on disk called the "main database file". During a transaction, SQLite stores additional information in a second file called the "rollback journal", or if SQLite is in WAL mode, a write-ahead log file. 1.1. Hot Journals If the application or host computer crashes before the transaction completes, then the rollback journal or write-ahead log contains information needed to restore the main database file to a consistent state. When a rollback journal or write-ahead log contains information necessary for recovering the state of the database, they are called a "hot journal" or "hot WAL file". Hot journals and WAL files are only a factor during error recovery scenarios and so are uncommon, but they are part of the state of an SQLite database and so cannot be ignored. This document defines the format of a rollback journal and the write-ahead log file, but the focus is on the main database file. 1.2. Pages The main database file consists of one or more pages. The size of a page is a power of two between 512 and 65536 inclusive. All pages within the same database are the same size. The page size for a database file is determined by the 2-byte integer located at an offset of 16 bytes from the beginning of the database file. Pages are numbered beginning with 1. The maximum page number is 4294967294 (232 - 2). The minimum size SQLite database is a single 512-byte page. The maximum size database would be 4294967294 pages at 65536 bytes per page or 281,474,976,579,584 bytes (about 281 terabytes). Usually SQLite will hit the maximum file size limit of the underlying filesystem or disk hardware long before it hits its own internal size limit. In common use, SQLite databases tend to range in size from a few kilobyte...