.DB-SHM 文件扩展名

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.

注: 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.