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Write-Ahead Log (WAL) is a mechanism that ensures data reliability and integrity in storage systems.

The idea is that before changes are applied to the main data, they are first recorded in a special journal (log). This allows, in case of failure or crash, to restore the system state by applying or rolling back operations from the log.

Example:

• When updating a record, the new version is first written to the WAL.
• After successful logging, the changes are applied to the main database.
• If the system crashes, upon restart, the WAL is read and incomplete operations are restored.

This approach guarantees the atomicity and durability of transactions.