AI engineering glossary · SQL databases
What is WAL (write-ahead log)?
Write-ahead log (also called WAL, Redo log): A durability technique where every change is first appended to a sequential log on disk before the data pages are changed. After a crash, the database replays the log to restore committed work. It also underpins replication.
Write-ahead log: an example
The server crashes after a commit but before data pages are written; on restart, the log is replayed and the committed change reappears.
Related terms
More SQL databases terms
Where you learn it
Write-ahead log is part of the AI Engineering Program, which teaches it with notes, a hands-on lab and an exam. The first lesson is free.