Hacker News Reader

What do you mean clearly laid out? This is the only mention of fsync I could find through google or their own search function.

https://clickhouse.yandex/docs/en/operations/settings/settin...

View on HN

The title of the page might be a little snarky, but it's in the introduction that transactional queries are not supported:

https://clickhouse.yandex/docs/en/introduction/features_cons...

Sure it's not specifically about `fsync` but presumably this is what the consumer of the database actually wants to know.

Fsync is not synonymous with transactions. Not using fsync anywhere means there's a wide window that can be over 10 minutes long when data can be lost when a server gets an unplanned shutdown.

Btw, it should be easy adding fsync to ClickHouse. For instance VictoriaMetrics uses similar file format as ClickHouse, and it issues proper fsyncs at least every second, so it may lose only the last second of data on unclean shutdown such as OOM, hardware reset or `kill -9`. [1], [2].

[1] https://medium.com/@valyala/wal-usage-looks-broken-in-modern...

[2] https://medium.com/@valyala/how-victoriametrics-makes-instan...

Reply on news.ycombinator.com