`acks = 1 behaviour`

Hello everyone! Can you please tell me if the setting is acks = 1, will Kafka wait for writing to disk or give an OS task and immediately return the result to the producer?

> Note that durability in Kafka does not require syncing data to disk, as a failed node will always recover from its replicas.

Acks=1 means the leader has positively acknowledged that it received the message and “wrote” it to disk. The nuance here is that “writing” to disk is handled by the OS. Meaning the jvm tells the OS, hey write this for me please. Kafka only calls fsync() every 10seconds by default.

Data writen to disk is only actually flushed to the disk when fsync is called

Thank you very much, very useful.

And what setting for 10 seconds are you talking about, not about [flush.ms](http://flush.ms) ?

I don’t suggest you change that

If you increase the flush rate your performance will dramatically decrease.