Saturday, February 13, 2010

Database time (DB TIME)

Database time (DB TIME)
The objective of database tuning is to reduce database time. In this way, you can
improve the overall response time of user transactions in the application.

The most important time model statistic is database time (DB time). Database time
represents the total time spent in database calls, and is an indicator of the total instance
workload. Database time makes up a portion of an application's overall user response time.
Database time is calculated by aggregating the CPU time and wait time of all active sessions
(sessions that are not idle). For anydatabase request, the CPU time is the sum of the
time spent working on the request,while the wait time is the sum of all the waits for
various database instance resources.DB time does not include time spent on background
processes such as PMON.

The CPU time spent by thedatabase processing the request and the wait time spent
waiting for the database are considered DB time.

Note: DB time is measured cumulatively from when the instance
started. Because DB time combines times from all non-idle user
sessions, DB time can exceed the time elapsed since the instance
started. For example, an instance that has run 5 minutes could have
four active sessions whose cumulative DB time is 20 minutes.

you can find DB time with this query's

FROM v$sess_time_model
WHERE stat_name = 'DB time';

select * from V$SYS_TIME_MODEL

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