What is Durability in ACID? How is it achieved in PostgreSQL?

The Durability principle in ACID guarantees that after a transaction successfully completes, its changes will be saved in the database and not lost even in case of failures, such as power outages or system crashes.

In PostgreSQL, this is achieved through the WAL (Write-Ahead Logging) mechanism. Before changes are applied to the main data, they are written to a transaction log (WAL). This log is stored on disk and ensures data recovery after failures. Thus, even if the system crashes, upon restart, PostgreSQL will apply the records from the WAL to restore the database to the state of the last successful transaction.