All resources affect CPU activity. As a database or system administrator, there are only a few things you can do to more efficiently use the CPU resources of your machine. The major consumer of CPU resources for your system should be the application code. Therefore, the greatest impact on CPU consumption can be made with application changes. Other resources are affected by application code as well, but there are things that you can do as an administrator to minimize problems associated with other resources. This is not the case with CPU resources. Slow disks can increase CPU activity by increasing the waits on I/O. If there is significant context switching, system delay time will increase. CPU activity is divided into four categories:
User time — The amount of time spent performing user tasks, such as running applications and database servers.
System time — The amount of time devoted to system overhead such as paging, context switches, scheduling, and various other system tasks.
Wait on I/O time — The amount of time the CPU is waiting for another resource (such as disk I/O).
Idle time — The amount of unallocated time for the CPU. If there are no jobs in the process queue and the CPU is not waiting for a response from some other resource, then the time is logged as idle. On some systems, such as Windows, wait on I/O is logged as idle. This is because the CPU is idle and waiting for a response. However, this time does not accurately reflect the state of performance on the system.
User time — The amount of time spent performing user tasks, such as running applications and database servers.
