DB Time

DB Time = DB Wait Time + DB CPU Time

Tuning is not just about reducing waits. It aims at improving end-user response time and/or minimizing the average resources used by each request.

Sometimes these go together, but in other cases there is a trade-off (for example, with a parallel query). In general, you can say that tuning is the avoidance of consuming or holding resources in a wasteful manner.

Any request to the database is composed of two distinct segments: a wait time (DB wait time) and a service time (DB CPU time). The wait time is the sum of all the waits for various database instance resources. The CPU time is the sum of the time that is spent actually working on the request. These times are not necessarily composed of one wait and one block of CPU time. Often processes will wait a short time for a DB resource and then run briefly on the CPU, and do this repeatedly.

Tuning consists of reducing or eliminating the wait time and reducing the CPU time. This definition applies to any application type, online transaction processing (OLTP) or data warehouse (DW).

Note: A very busy system shows longer DB CPU times and this can inflate other times.

CPU and Wait Time Tuning Dimensions