Write-ahead log.

also: WAL · write-ahead logging · write ahead log · WALs

An append-only log every change is written and fsynced to before the data files are updated, so a crash can be replayed safely.

the two-minute refresher

Updating data in place is not atomic: a crash mid-write corrupts it.
So: append to the WAL, fsync, then apply to data files; checkpoint and truncate later.
Recovery replays committed entries from the last checkpoint and discards uncommitted ones.
Sequential appends are fast, and the same log feeds replication and change data capture.

also: WAL · write-ahead logging · write ahead log · WALs

An append-only log every change is written and fsynced to before the data files are updated, so a crash can be replayed safely.

Updating data in place is not atomic: a crash mid-write corrupts it.
So: append to the WAL, fsync, then apply to data files; checkpoint and truncate later.
Recovery replays committed entries from the last checkpoint and discards uncommitted ones.
Sequential appends are fast, and the same log feeds replication and change data capture.