Interpret DB CPUwait event (top 5 wait event AWR)

Question

Hi,
Can anyone tell me how to read the table below especially the "DB CPU" section,
Is it right to say that 41.71% of time was consumed waiting for CPU?? this is urgent
Event                     Waits           Time(s)      Avg wait (ms)      % DB time      Wait Class
db file sequential read      300,835      1,483           5           58.42           User I/O
DB CPU                     1,059                     41.71
reliable message           9,499           18           2           0.71           Other
PX Deq: Slave Session Stats      6,506           11           2           0.43           Other
gc cr grant 2-way           26,218           6           0           0.25           Cluster

Answer 1

user589420 wrote:
Hi,
Can anyone tell me how to read the table below especially the "DB CPU" section,
Is it right to say that 41.71% of time was consumed waiting for CPU?? this is urgent
Event                           Waits  Time(s)  Avg wait (ms)  % DB time  Wait Class
db file sequential read       300,835    1,483              5      58.42  User I/O
DB CPU                                   1,059                     41.71
reliable message                9,499       18              2       0.71  Other
PX Deq: Slave Session Stats     6,506       11              2       0.43  Other
gc cr grant 2-way              26,218        6              0       0.25  Cluster
When posting information to the forum that includes critical spaces, like the above, use a { code } tag (without spaces) before and after the information.
I do not understand why this question is an urgent problem.
It is incorrect to state that 41.71% of the time was consumed waiting for the CPU. When an Oracle process is running on the CPU, it is officially not waiting. It causes a bit of confusion having the CPU time consumed listed among the top 5 wait events, but as long as you understand why it is in the top 5 list, it almost makes sense for it to be included.
The DB CPU statistic is listed as 1,059 seconds. If the duration of this report is 1 hour, that is 3,600 seconds of total time. If there is a single CPU in the server, there are 3,600 CPU seconds available in the time period, indicating that the server's CPU on average was 29.4% busy. If there were 12 CPUs in the server, there were 43,200 CPU seconds available in the time period, indicating that on average the CPUs were 2.5% busy. Does this mean that there was a problem, or was this OK, or is there not enough information? Just because on average the CPUs are not busy, that does not mean that there were not periods of intense CPU competion, where in fact there was a temporary shortage of available CPU time for processing.
The DB Time statistic is supposed to be an indication of work performed by the instance on behalf of the user sessions. It is the accumulation of CPU time consumed by foreground sessions plus the accumulated sum of all non-idle wait events consumed by foreground sessions. Blog articles that might be of interest to you:
http://hoopercharles.wordpress.com/2010/01/13/working-with-oracle-time-model-data/
http://hoopercharles.wordpress.com/2010/02/05/faulty-quotes-6-cpu-utilization/
Charles Hooper
Co-author of "Expert Oracle Practices: Oracle Database Administration from the Oak Table"
http://hoopercharles.wordpress.com/
IT Manager/Oracle DBA
K&M Machine-Fabricating, Inc.