If Web Server must run in low-memory situations, reduce the thread limit to a bare minimum by lowering the value of the Maximum Threads setting on the configuration's Performance Tab ⇒ HTTP sub tab. You can also set it with wadm set-thread-pool-prop command's max-threads property.
The server automatically selects many server defaults based on the system resources, for optimal performance. However, if the server's chosen defaults are not suited to your configuration, you can override them. For more information about how to tune the server to obtain a smaller memory footprint, see Large Memory Footprint.
Web applications running under stress might sometimes result in the server running out of Java VM runtime heap space, as seen in the java.lang.OutOfMemoryError messages in the server log file. There can be several reasons for this, including excessive allocation of objects, and such behavior can affect performance. To address this problem, profile the application. Refer to the following HotSpot VM performance FAQ for tips on profiling allocations (objects and their sizes) of your application:
If your application runs out of maximum sessions as evidenced by a “too many active sessions” message in the server log file, and results in the container throwing exceptions, application performance will be impacted. To address the situation, consider the session manager properties, and the session idle time. Note that JSPs have sessions enabled by default.