.DB-SHM File Extension

SQLite's Write-Ahead Logging (WAL) mode is a journaling mode designed to improve database writing performance while maintaining data integrity. Typically, any changes made to a database are written directly to the main database file.

However, in WAL mode, the SQLite database engine automatically generates a .DB-WAL file to store data writes, allowing the main database to remain unaltered during the write process. The engine also generates a DB-SHM file to store data for tracking reader-writer states, checkpoint statuses, and transaction control, allowing multiple connections to the main database to synchronize. For example, if you have a primary database file named mydb.db, the SQLite engine may automatically generate mydb.db-shm and mydb.db-wal files while the database is in use.

By generating DB-WAL and DB-SHM files in WAL mode, the SQLite engine keeps the database accessible for reading by other processes while writes are pending, significantly improving performance in applications with high read-write demands. Additionally, DB-SHM and DB-WAL files may appear in an application's data storage directories, particularly in apps that utilize SQLite databases for handling large amounts of data or complex data operations across different processes.

NOTE: SQLite introduced WAL mode in 3.7.0 in July 2010.

You should not attempt to open DB-SHM files since they serve as supplemental, non-essential files for the primary database. When the application or database connection is closed, you can safely delete these temporary files if they persist.