Performance slow about too many call to auth func

[cszxc]

For some reason I debug the authentication_api.c to intergrate Mantis to xoops. When I change to use DB to check user login, the all system is slower!
I debug it and find even in a all-new installed program, when I select "View all bug", show nothing bug, but the func auth_is_user_authenticated() is called oevr 200 times! Why? I think only check it at beginning! I change it func to user global var(only test), and the speed is very obviously.
Who can tell me why? I think it can be optimized!