WAL

A Write Ahead Log is an append only data structure prevelantly used by database systems. It allows a data system to serve a high volume of write requests durably without sacrificing performance (writing multiple disk pages).

The WAL is usually written to the underlying database file (commonly a B-Tree) on startup or a regular interval.

Besides durability and performance a WAL is useful as a hook for implementing logical replication (CDC) as it contains ordered change events.