Write-Ahead Logging is a technique used to ensure the data integrity of PostgreSQL databases. It helps in maintaining the resilience or the reliability of the database. Write-ahead logging is a method wherein any changes and actions in the database are logged in a transaction log prior to the updating or modification of the database. In case there is a database crash, this feature helps the in providing the log of the database changes. In addition, it also helps the user in resuming work from where it was discontinued, after the crash.