olemus
andmebaasi iga muudatuse logimine enne selle tegemist
= recording the changes in log before they are actually done in the database

ülevaateid
https://en.wikipedia.org/wiki/Write-ahead_logging
https://www.quora.com/What-is-the-difference-between-journal-and-write-ahead-log-in-filesystems
http://work.tinou.com/2012/09/write-ahead-log.html