What is "write-ahead logging" (WAL) and why is it important for durability?

A WAL is a feature that prevents any writes from occurring until the database is backed up B WAL requires that changes be recorded in a sequential log before being applied to the actual data files, so that after a crash the database can replay the log to recover committed transactions and undo uncommitted ones C WAL is only used for read replicas, not the primary database D WAL eliminates the need for transaction commits