Multiplayer persistent data on the server

Working on an MMO… using UNET with a dedicated server.
I’d like to persist player data ( such as current equipment and stats ) as well as various game objects’ data (position, state, Ect).
I’m having a difficult time finding good information on this subject, surprisingly… I can’t find anything about persistence in the Unity manual for multiplayer.

What are some of the ways this is usually done?
I know Unity has built in ways to save user data but would this be ideal for an MMO, potentially saving thousands of objects’ positions per second?

I was thinking of maybe using PHP/Mysql but I can’t imagine running that many queries would be a good method? But maybe there doesn’t have to be that many queries… perhaps saving object data is something that’s only done once a minute or perhaps even a longer duration…

UPDATE: The only way I can think of at this time is updating every new spawned item’s position and state via PHP/Mysql… I will attempt this system

But maybe there doesn’t have to be
that many queries… perhaps saving
object data is something that’s only
done once a minute or perhaps even a
longer duration…

That’s correct. You store this info in the dedicated external database’s table, using SQL query, through php or c# or whatever language you use for such queries