Determine which problem to tune first. In the performance reports, you
see many statistics; even a well-tuned database shows a set of top wait events.
The Oracle server provides a set of wait event statistics for processes that
are idle or waiting. The Oracle server also records CPU utilization for
processes that are running. To determine the impact of a particular event, it
must be compared with the overall time spent.
Each request to the database server has a response time consisting of a
wait time and a service time. The service time is the time spent actively
working on the request (CPU time). The wait time is by definition the time
waiting for any reason. Both service time and wait time may be tuned.
To tune
the service time something has to change: the processing, the SQL, the access
path, or the data storage structure.
Wait times can be tuned by reducing
contention for the resource where the wait is occurring.
Each server process is typically in one of three states:
- Idle: Waiting for something to do (sleeping)
- Running code: Using the CPU or in a run queue
- Waiting (blocked):
- For some resource to become available
- For a requested activity to complete
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