If Sun Java System Web Server must run in low-memory situations, reduce the thread limit to a bare minimum by lowering the value of RqThrottle. Also, you may want to reduce the maximum number of processes that the server will spawn by lowering the value of the MaxProcs value.
Your web applications running under stress may sometimes result in the server running out of Java VM runtime heap space, as can be seen by java.lang.OutOfMemoryError messages in the server log file. There could be several reasons for this (such as excessive allocation of objects), but such behavior could affect performance. To address this problem, you would need to profile the application. Refer to the following HotSpot VM performance FAQ for tips on profiling allocations (objects and their sizes) of your application:
At times your application could be running out of maximum sessions (as evidenced by the "too many active sessions message" in the server log file), which would result in the container throwing exceptions, which in turn impacts application performance. A due consideration of session manager properties, session creation activity (note that JSPs have session enabled by default), and session idle time would be needed to address this situation.