Resolved Server save data

I am making a turn based client - server game.
The idea is that when a player do an action, a RPC is sento to the server that validate and applay it.
The player send its identifier, the match identifier and the action identifier, so the serve can know what player do what in what match.

I think to avoid data losses in case of server shutdown, to use some data persistence.
I found some different ways:
- External DB running in the server
- DP embedded in the program
- Data Serialization on file system

What should I use to perform data persistence?
How frequently should I save data for every single match?

 

Use what does the job. How often do you expect a server to shutdown prematurely or crash? Better try to avoid that situation as much as possible.

Frequency: once per turn, since it‘s turn-based.

 

Thanks.
I think the better way is to use a DB. Some recommended for Unity? I think to use SQLite.
Do you know better solutions?