This page is for tips and techniques for troubleshooting a memory-starved uPortal.
Are channels problematic? IMultithreadeds?
You should also look at what channels you have included in your site and if possible what "type" of channels they are in terms of uPortal's multi-threaded versus single threaded channel interfaces. We had a customer using a channel that extended BaseMultithreadedChannel and didn't pass the handle event calls back up to the super class. If that doesn't happen then the BaseMultithreadedChannel hangs onto state objects indefinitely and leads to these errors every few hours. They have since removed that channel and the problem went away.
Is Tomcat / the JVM configured to use an appropriate amount of memory?
In your Tomcat, you need to up the settings of -Xmx and probably -Xms. These are JAVA_OPTS in your catalina.sh or catalina.bat. I believe there's more info on the uPortal Wiki or the Tomcat documentation pages (jakarta.apache.org, I think). See also the page on JVM Configurations and this thread.