The transaction is written to the write ahead log and fsync'd before the client is told OK. It may not have made it to the table storage on disk yet (but will

The transaction is written to the write ahead log and fsync'd before the client is told OK. It may not have made it to the table storage on disk yet (but will be in memory), but if there's a crash the WAL can be replayed to recover safely - you'll see postgres do this if it crashes from OOM or gets restarted unexpectedly