Write ahead logging

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

In a system using WAL, all modifications are written to a Database 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 algorithm. The other obvious way to implement atomic update is with shadow paging, which is not in-place. The main advantage of doing updates in-place is it reduces the need to modify indexes and block lists.

ARIES is a popular algorithm in the WAL family.