[SR-Users] BasicKamailio DB question

Hi all, excuse the basic nature of my question, I'm just starting out. I've read in a tutorial that it is possible to connect from asterisk to Kamailio and for asterisk to use the Kamailio db for authentication. However, I also read that it is possible to connect to astereisk from Kamailio for retrieving auth data. My question is this... If Kamailio uses the db on a remote asterisk server to retrieve usernames and password info how do you set Kamailio to use multiple databases as you may ultimately have multiple asterisk servers? As far as I could see there is only 1 db typically in the config file. Also, which is the most common configuration and why would one choose one over the other? Thanks in advance.