You can tune the WebSphere Portal caches to improve the portal performance. The WebSphere Portal Cache Viewer can help you determine which caches might be worth tuning to improve the performance of your portal.
The Cache Viewer shows you the state of all WebSphere Portal caches. In addition, it provides tuning suggestions for those caches. For more information regarding portal tuning and portal cache architecture, consult the WebSphere Portal Performance Tuning Guides. The guides are available as part of the WebSphere Portal Family wiki.