Write ahead logging

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In computer science, write ahead logging (WAL) is a family of techniques for providing atomicity and durability (two of the ACID properties) in database systems.

In a system using WAL, all modifications are written to a log before they are applied to the database. Usually both redo and undo information is stored in the log.

The motivation for WAL is to allow updates of the database to be done in-place. Another way to implement atomic updates is with shadow paging, which is not in-place. The main advantage of doing updates in-place is that it reduces the need to modify indexes and block lists.

ARIES is a popular algorithm in the WAL family.

In file systems, WAL is often called Journaling.