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AWR DB Time tips

Oracle Database Tips by Burleson Consulting

May 20, 2016

Question: What is the DB Time metric in an AWR report and how do I generate the DB Time directly from the AWR tables?  I need to see the AWR DB Time and understand this metric.

On a four CPU system ( 4 CPU CORE ) , for one hour elapsed time, what is the maximum amount of DB Time that can be accumulated in an AWR report for the hour? 

Answer:  First, read these important notes on the DB Tme metric.

The DB Time is a time model statistic that is the sum of all Oracle process' CPU consumption plus the sum of non-idle wait time. When optimizing Oracle databases, we focus on reducing the processing "time", usually by tuning SQL statements.  

WORKLOAD REPOSITORY report for

DB Name         DB Id    Instance     Inst Num Startup Time    Release     RAC
------------ ----------- ------------ -------- --------------- ----------- ---
FINONE        1252548811 mydb              1 13-Dec-12 22:10 11.2.0.3.0  NO

Host Name        Platform                         CPUs Cores Sockets Memory(GB)
---------------- -------------------------------- ---- ----- ------- ----------
MYPROD           AIX-Based Systems (64-bit)         24    12              80.00

              Snap Id      Snap Time      Sessions Curs/Sess
            --------- ------------------- -------- ---------
Begin Snap:     25130 15-Dec-12 03:00:39       425      12.2
  End Snap:     25131 15-Dec-12 04:00:45       430      14.7
   Elapsed:               60.09 (mins)
   DB Time:              298.22 (mins)

The formula for DB Time can be expressed as CPU time plus non-idle wait time:

         DB Time = DB CPU + non_idle_wait_time

and it follows that

         non_idle_wait_time = DB Time - DB CPU

This "time" in AWR is the same as DB Time and it is the same as the DB Time statistic name in v$sess_time_model and v$sys_time_model. The maximum DB Time metric in AWR is influenced by these metric values:

  • The number of connected sessions (the max is the "sessions parameter in the init.ora (spfile)
  • The number of CPU's (cpu_count parameter) on the server
  • The number of parallel processes running

As we see, the DB Time will vary wildly depending on the amount of activity on the database.

For a SQL statement, the db time does not really apply because db time is a system-level metric:

Statistic Name                     Time (s) Percent of Total DB Time
---------------------------------- -------- ------------------------
DB time                                 169
sql execute elapsed time                156                       93
DB CPU                                  153                       90
PL/SQL execution elapsed time            77                       46
background cpu time                      53                       31
parse time elapsed                        6                        4
hard parse elapsed time                   4                        3
connection management call elapsed time   0                        0

 

This script will display the DB Time for a specific AWR snapshot:

SELECT * FROM
(
SELECT
A.INSTANCE_NUMBER,
LAG(A.SNAP_ID) OVER (ORDER BY A.SNAP_ID) BEGIN_SNAP_ID,
A.SNAP_ID END_SNAP_ID,
TO_CHAR(B.BEGIN_INTERVAL_TIME,'DD-MON-YY HH24:MI') SNAP_BEGIN_TIME,
TO_CHAR(B.END_INTERVAL_TIME ,'DD-MON-YY HH24:MI') SNAP_END_TIME,
ROUND((A.VALUE-LAG(A.VALUE) OVER (ORDER BY A.SNAP_ID ))/1000000/60,2) DB_TIME_MIN
FROM
   DBA_HIST_SYS_TIME_MODEL A,
   DBA_HIST_SNAPSHOT       B

WHERE
A.SNAP_ID = B.SNAP_ID AND
A.INSTANCE_NUMBER = B.INSTANCE_NUMBER AND
A.STAT_NAME = 'DB time'
)
WHERE DB_TIME_MIN IS NOT NULL AND DB_TIME_MIN > 0
ORDER BY 2 DESC;

 

 


   
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Note: This Oracle documentation was created as a support and Oracle training reference for use by our DBA performance tuning consulting professionals.  Feel free to ask questions on our Oracle forum.

Verify experience! Anyone considering using the services of an Oracle support expert should independently investigate their credentials and experience, and not rely on advertisements and self-proclaimed expertise. All legitimate Oracle experts publish their Oracle qualifications.

Errata?  Oracle technology is changing and we strive to update our BC Oracle support information.  If you find an error or have a suggestion for improving our content, we would appreciate your feedback.  Just  e-mail:  and include the URL for the page.


                    









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