socket.io nodejs : use database to store all sockets clients?

At the moment, i store sockets for each client to emit.

clients[myID] = socket;

but i wonder if there is a lot of user it will be a problem. Is that it can be much to store clients in database like express store sessionID (using redis) ?

(i must to stock the entire socket to make it work ? so, it's big !)

What's the best way ?

I saw there was some time that could be do something like that:

sio.set('store',...

what is it ? How to use it ?

Or, i can store using redis normally ?

Thanks !