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Wait Class - DB CPU [message #637401]

Sun, 17 May 2015 02:55

karthik4u
Messages: 36
Registered: September 2006
Location: CHENNAI

Member

We have collected AWR report during huge process which runs for nearly 4 hrs and in 30 parallel sessions.

From AWR report found that DB CPU wait class as follow

Wait Classes by Total Wait Time:

----
Wait Class Waits Total Wait Time (sec) Avg Wait (ms) % DB time Avg Active Sessions
DB CPU 107,579 63.8 6.0
----

How to reduce this Total Wait Time? What we need to check for the same in AWR report?

Kindly advice.

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Re: Wait Class - DB CPU [message #637402 is a reply to message #637401]

Sun, 17 May 2015 02:58

karthik4u
Messages: 36
Registered: September 2006
Location: CHENNAI

Member

Wait Classes by Total Wait Time:

----
Wait Class---Waits---Total Wait Time (sec)----Avg Wait (ms)----% DB time----Avg Active Sessions
DB CPU------- ---107,579------------------ ---- 63.8--------6.0
----

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Re: Wait Class - DB CPU [message #637403 is a reply to message #637402]

Sun, 17 May 2015 03:50

Michel Cadot
Messages: 67919
Registered: March 2007
Location: Nanterre, France, http://...

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Account Moderator

DB CPU is ot a real wait class, it is the time you spent on CPU that is actually working.
If you want to reduce it then reduce the work you ask the database to do.

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Re: Wait Class - DB CPU [message #637427 is a reply to message #637402]

Sun, 17 May 2015 09:06

John Watson
Messages: 8577
Registered: January 2010
Location: Global Village

Senior Member

63.8% is not bad for CPU time. I would be nice to get it a bit higher, if you think that there is a problem. But you do have to define the problem. I do not think that any of your users have telephoned you to complain that "DB CPU wait class percentage is bad". What are they complaining about?

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Re: Wait Class - DB CPU [message #637459 is a reply to message #637401]

Mon, 18 May 2015 09:08

bpeasland
Messages: 51
Registered: February 2015
Location: United States

Member

Your SQL statement's runtime is the sum of the time on the CPU and the sum of the total wait time. Many people focus on the wait time end of the equation. But I've seen many SQL statements that have a lot of CPU time and very little wait time.

Remember that there are two types of I/O, physical and logical. Physical I/O will show up as different wait events. Logical I/O will show up as CPU cycles. Reduce the logical I/O and the CPU consumption will go down. I often see this when a query is showing a very high number of logical reads, for example, the query is performing too many full table scans that the tables involved are all in the Buffer Cache.

Cheers,
Brian

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Re: Wait Class - DB CPU [message #637460 is a reply to message #637401]

Mon, 18 May 2015 09:22

BlackSwan
Messages: 26766
Registered: January 2009
Location: SoCal

Senior Member

>We have collected AWR report during huge process which runs for nearly 4 hrs and in 30 parallel sessions.

How was 30 parallel session deemed as optimal?
Why not a higher or lower number?

How many CPU/core exist in the server system?

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Re: Wait Class - DB CPU [message #637463 is a reply to message #637401]

Mon, 18 May 2015 10:15

Lalit Kumar B
Messages: 3174
Registered: May 2013
Location: World Wide on the Web

Senior Member

karthik4u wrote on Sun, 17 May 2015 13:25

30 parallel sessions.

30 parallel sessions? Seriously?

I mean for 30 parallel sessions, you need to have a big time hardware and infrastructure. Have a look at this and this.

[Updated on: Mon, 18 May 2015 10:21]

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