HiveMQ seems to provide various options to persist session data, including QoS 1/2 messages.
The persistence options are listed here:
- File persistence
- In-Memory persistence
By default, HiveMQ will use the file persistence, which saves all the data to the disk so it can be retrieved at any time.
In order to guarantee consistency of data between broker restarts, HiveMQ uses disk persistence by default. That means that even if the broker stops or crashes, all data will be preserved and after a restart the broker can continue its operation as if nothing happened.