From WLS 9.0 series onwards,server has a single thread pool for requests from all applications. Similarly, all pending work is enqueued in a common priority-based queue. The thread count is automatically tuned to achieve maximum overall throughput.
One of the major differences between execute queues and the new thread scheduling model is that the thread count does not need to be set. In earlier releases, customers defined new thread pools and configured their size to avoid deadlocks and provide differentiated service. It is quite difficult to determine the exact number of threads needed in production to achieve optimal throughput and avoid deadlocks. WebLogic Server 9.0 is self-tuned, dynamically adjusting the number of threads to avoid deadlocks and achieve optimal throughput subject to concurrency constraints.
The maximum threads constraint can be used to limit the maximum number of concurrent threads given to all WorkManagers that share the constraint.This constraint should be used in very special cases and should not be confused with the thread count parameter in execute queues. The minimum threads constraint takes an integer value that specifies the number of threads that should be assigned to this constraint to prevent server-to-server deadlocks.