An append-only file records Redis mutations for recovery, but choosing AOF is not the same as promising that no acknowledged write can ever disappear. Durability depends on the fsync policy, effective configuration, storage behavior, and which failure you mean. Start with a recovery objective rather than the reassuring word “log.” ...
A checkpoint records progress that lets a database recover without treating its entire log history as outstanding work. The exact operation depends on the engine. PostgreSQL synchronizes the data changes required for a checkpoint and establishes a redo starting point. SQLite in WAL mode transfers eligible committed page frames from its WAL into the main database file. Neither operation is simply another name for transaction commit. ...
Write-ahead logging lets a database make a transaction durable without immediately flushing every table and index page that transaction changed. In PostgreSQL, the log records needed to recover a page must be durable before that page is written to storage. Normal synchronous commit also waits for the commit record to be flushed. Buffered table changes and durable log records therefore advance through different paths. ...