slave db server setup
 

I have looked both here and on vbulletin.org but am unable to find any definite information regarding how vb treats the slave db server.

Do I need to replicate the entire vbulletin database?
It seems as though the slave is setup to handle any read requests that come its way (doens't do write), but that means that it could also load up threads and such. It would seem more ideal just to have the slave do all the searching and let the main db do all the read/write for threads, etc.

Can anyone shed some light on the vBulletin 3.8 slave db functionality?

Thanks