DB-SHM File – What is .db-shm file and how to open it?
DB-SHM File Extension
SQLite Database Shared Memory File – file format by SQLite
The DB-SHM file extension is associated with the SQLite database system developed by SQLite, and it is used for shared memory files that facilitate data sharing between multiple processes.
SQLite Database Shared Memory File (DB-SHM)
A DB-SHM file is a file used by SQLite, a lightweight, self-contained and embeddable database engine, to store shared memory for a database connection. It enables multiple processes or threads to access the same database concurrently, enhancing performance and efficiency. The shared memory segment contains a copy of the database pages, allowing for faster data retrieval and updates by reducing the need for physical I/O operations.
DB-SHM files are crucial for maintaining data integrity and consistency in multi-threaded or multi-process environments. They ensure that all processes accessing the database see the same version of the data and any changes made by one process are immediately visible to others. This shared memory mechanism optimizes database performance and eliminates potential data inconsistencies or race conditions that could arise in a multi-threaded environment.
What is a DB-SHM File?
A DB-SHM file is a SQLite Database Shared Memory File used by SQLite, an open-source SQL database management system. It is a temporary file that stores database metadata, such as table definitions, indexes, and other information necessary for the database to function. DB-SHM files are created and managed by the SQLite library and are used to improve database performance by sharing the metadata among multiple connections to the same database.
Opening DB-SHM Files
DB-SHM files are not meant to be opened or edited directly by users. They are only accessible by the SQLite library and are automatically created and deleted as needed. Manipulating or modifying DB-SHM files can corrupt the database, leading to data loss or inaccessibility. Therefore, it is not recommended to attempt to open or modify these files manually. Instead, users should interact with the database through standard SQLite interfaces and commands.
sqlite3 creates this type of file to support shared memory among multiple processes. The functions using the shared memory system are:
- “sqlite3_initialize()
- “sqlite3_shutdown()
- “sqlite3config(SQLITECONFIGMMAPSIZE,…)”
- “sqlite3config(SQLITECONFIG_PAGECACHE,…)
- “sqlite3config(SQLITECONFIGCKPTPENDING,…)”
- “sqlite3config(SQLITECONFIGCKPTFULLFSYNC,…)”.
The shared memory file is opened using mode 0600 (read/write) permissions. If this is not possible, then the shared memory file is opened in read-only mode. The shared memory file is not visible in the file-system, but its size can be examined with the Linux “lsof” program. The shared memory file is deleted when all processes using the shared memory have closed their database connections.
This “lock” file is created by sqlite3 to establish a lock on the database file. The file extension .lock is appended to the database file name. The lock file is deleted when the database connection is closed.