Background Information:
I installed DNN 3.1.1 with 20 parent portals using UCanUse PortalMapper to allow users to have a single sign-on.  This was 11 months ago.  In the past two months the DNN portals were experiencing sever delay problems with the initial page taking 15-30 seconds to render, another delay for the login screen to display, yet another delay for user authentication, and all subsequent page access.  I tried all the recommended speedups:  Blowery compression, cachiing, IIS HTTP compression enable, and still no performance improvement.

Solution:
Accessing the Admin > Log Viewer resulted in over 70 pages and trying to access the Admin > Site Log resulted in a page error.  I used SQL Enterprise Manager an discover that the the SiteLog and EventLog tables each had over 700 entries.  I deleted older records from the tables and found that the perfomance was back to normal.  The two Admin pages also displayed normally.

However...  I feel that I only fixed the symptom and not the problem...  Does anyone know how to set the limits to the two tables to keep them from growing?  Replys would be greatly appreciated.

to improve your performance to go host settings and increase your caching to medium or heavy.

also make sure theres not any unescessary scheduled processes going on.

Lots of things can slow down your site, including heavy skins.

Just remember before you upgrade, make a backup....