Oracle DB time tips

Oracle Consulting Tips by Burleson

The DB time Oracle metric is the amount of elapsed time (in microseconds) spent performing Database user-level calls. This does not include the time spent on instance background processes such as PMON.

ADDM’s goal is to improve the value of a statistic called DB time. DB time is a value that Oracle calculates to indicate the cumulative time that is spent processing user requests. ADDM’s goal is to reduce the overall DB time value, and it does not target individual users or user response times, and thus the DB time it uses is an aggregate value of overall system CPU and wait times.

The goal for tuning Oracle process should be to reduce to minimum CPU time and Wait time so that more transactions can be processed. This is done by tuning the SQL:

DB Time = CPU time + I/O time + Non-idle wait time

DB time is total time spent by user processes either actively working or actively waiting in a database call.

From this formula we can conclude that database requests are composed from CPU (service time, performing some work) and wait time (session is waiting for resources).

select
   to_char(begin_time,'dd.mm.yyy hh24:mi:ss') begin_time,
to_char(end_time,'dd.mm.yyy hh24:mi:ss') end_time,
intsize_csec interval_size,
group_id,
metric_name,
value
from
   v$sysmetric
where
   metric_name = 'Database Time Per Sec';

Here is a DBV time query from v$sysmetric_summary:

select
   maxval,
   minval,
   average,
   standard_deviation
from
   v$sysmetric_summary
where
   metric_name = 'Database Time Per Sec';

Here is another query for DB time from the ASH table:

select
   count(*) DB_TIME,
from
   v$active_session_history
where
   session_type = 'FOREGROUND'
and
   sample_time between to_date('30032016 10:00:00','ddmmyyyy hh24:mi:ss')
and
   to_date('30032016 10:30:00','ddmmyyyy hh24:mi:ss');

You can see the current value of DB time for the entire system by querying the V$SYS_TIME_MODEL or you can see it for a given session by using the V$SESS_TIME_MODEL view as seen here:

select
   sum(value) "DB time"
from
   v$sess_time_model
where
   stat_name='DB time';

DB time
----------
109797