SQLite

Revision as of 00:49, 20 November 2021

SQLite is a self-contained, serverless, zero-configuration, transactional SQL database engine. The code for SQLite is in the public domain and is thus free for use for any purpose, commercial or private.

Write-Ahead Logging

Some versions of SQLite use write-ahead logging to store new changes to the database before they are written to the main database file, allowing a rollback of the current set of changes before they are committed. Database access uses both files to get the latest changed version even if part of it is still in the "WAL" file. This file is a separate file from the main database, using -wal at the end of the file extension so that it becomes .db-wal or .sqlite-wal. Also, a shared-memory file is often used for a hash-table index of the write-ahead log, with a .db-shm or .sqlite-shm extension.

Temporary Files

SQLite creates temporary files that, by default, begin with the prefix etilqs_ and have no file extension. The backstory:

** 2006-10-31:  The default prefix used to be "sqlite_".  But then
** Mcafee started using SQLite in their anti-virus product and it
** started putting files with the "sqlite" name in the c:/temp folder.
** This annoyed many windows users.  Those users would then do a 
** Google search for "sqlite", find the telephone numbers of the
** developers and call to wake them up at night and complain.
** For this reason, the default name prefix is changed to be "sqlite" 
** spelled backwards.  So the temp files are still identified, but
** anybody smart enough to figure out the code is also likely smart
** enough to know that calling the developer will not help get rid
** of the file.

Resources

• SQLite.org: The SQLite Database File Format
• Write-Ahead Logging
• How To Corrupt An SQLite Database File
• sql.js: Port of SQLite to JavaScript