Why large roster table takes more authentication time in openfire

Hi,
I need to know why large roster table degrades the performance of the openfire to a great extend.

I was facing the issue of high CPU consumption and authentication time of around 15s. Tried many things but could not solve it. Finally I deleted my “ofRoster” table and boom!! , everything is working great. Now my authentication time has fallen to 40ms.

FYI, My ofRoster table had crores of data. But I need to why is it affecting the performance of openfire to such a great extend?

Thanks in advance.