There is no correspondence between your operating system’s reports on CPU usage and Adaptive Server’s internal “CPU busy” information. It is normal for an Adaptive Server to exhibit very high CPU usage while performing an I/O-bound task.
A multithreaded database engine is not allowed to block on I/O. While the asynchronous disk I/O is being performed, Adaptive Server services other user tasks that are waiting to be processed. If there are no tasks to perform, Adaptive Server enters a busy-wait loop, waiting for completion of the asynchronous disk I/O. This low-priority busy-wait loop can result in very high CPU usage, but because of its low priority, it is generally harmless.
