What is SQLite SHM and WAL files?

Question

The WAL-Index File Format. The WAL-index or "shm" file is used to coordinate access to the database by multiple clients, and as a cache to help clients quickly locate frames within the wal file. Because the shm file is not involved in recovery, the shm file does not need to be machine byte-order independent.

What is a SQLite WAL file?

Write-Ahead Log (WAL) Files. A write-ahead log or WAL file is used in place of a rollback journal when SQLite is operating in WAL mode. As with the rollback journal, the purpose of the WAL file is to implement atomic commit and rollback.

What is a SHM file?

A DB-SHM is a temporary file created by SQLite, a compact database program often embedded into mobile and desktop applications. It is used by the database to store shared memory and is automatically created and maintained by SQLite. Such files are not intended to be opened manually.

What is a WAL file?

WAL is short for Write Ahead Log. WALs are used in nearly all modern RDBMS systems to provide durable and atomic transactions. Simply put, any transaction performed on the database is first written out as a WAL file, then applied to the actual on-disk table data files. WAL files are strictly sequential.

What is the SQLite file format?

What is a SQLite File? A file with . sqlite extension is a lightweight SQL database file created with the SQLite software. It is a database in a file itself and implements a self-contained, full-featured, highly-reliable SQL database engine.

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