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Tuning tries to identify bottlenecks that take too long and tries to reduce these bottleneck's time. These bottlenecks can be in the hardware (network, memory, cpu) and the software (application, operating system, database).
Generally, Oracle's time used for an operation (such as a select statement) to complete is composed of time executing (=CPU time) and time spent waiting (=Waiting time).
The aim of tuning is to reduce the sum of CPU time and waiting time. This sum is the response time for an operation.
CPU time can further be divided into
Due to the granularity of measurement, OS User time + OS System time might be greater than CPU used..
User time then can again be divided into:
Used CPU time can be found through v$sesstat, v$sysstat and v$mystat (
Oracle has a bunch of events that it can wait for.