Re: DB TIME in AWR

I think i got it now for DB time . Need some clarification for CPU time . how can we calculate CPU time

 Suppose 5 foreground sessions are active and executing long queries running for entire 15 minutes . CPU core is 4 .

In this case by definition :

DB Time = Total time in database calls by foreground sessions

             DB Time                   = 15 Minutes * 5 Active sessions
             DB Time                   =  75 Minutes

On Sun, May 22, 2016 at 4:52 PM, Iggy Fernandez <iggy_fernandez_at_hotmail.com> wrote:

> I believe that sessions does not include parallel processes which also
> contribute to DB time.
>
> However, the processes setting includes some processes that do not
> contribute to DB time.
>
> So sessions * elapsed time may be an underestimate whereas processes *
> elapsed time is an overestimate.
>
> re: CPU cores. You may be confusing "CPU time" and "DB time". DB Time is
> the "sum of the elapsed times of database calls by foreground sessions"
> (definition in the webinar) and is more than just CPU time. Therefore it is
> no related to cores or threads.
>
>
> ------------------------------
> From: dba.tyagisumit_at_gmail.com
> Date: Sun, 22 May 2016 16:30:43 +0530
> Subject: Re: DB TIME in AWR
> To: iggy_fernandez_at_hotmail.com
> CC: oracle-l_at_freelists.org
>
>
> Not an interview question :) I was going through the attached webinar *Who
> Ate My DB Time? Advanced Techniques For Database Performance Analysis*,
> got this question from one of the slide :
>
> *As per the doc answer is Number of ‘sessions’ * elapsed time . but want
> to know why cpu cores are not considered ?*
>
> *DB Time: Quiz*
>
> *Question: On a four CPU system, for one hour elapsed time, what **is the
> maximum amount of DB Time that can be accumulated? **Hint: How many
> sessions can wait in a queue?*
>
> *Answer: Number of ‘sessions’ * elapsed time*
> *.*
> *The maximum number of sessions that are on CPU or in a non-idle*
> *wait is the init.ora parameter ‘sessions’. If ‘sessions’ is 300 then:*
> *300 * 1 hour = 300 hours of DB Time*
>
> *Copyright © 2011, Oracle and/or its affiliates. All rights **reserved*
>
>
> On Sun, May 22, 2016 at 4:06 PM, Iggy Fernandez <
> iggy_fernandez_at_hotmail.com> wrote:
>
> There are many processes than there are sessions.
>
> My answer is processes * elapsed time
>
> From the documentation: "PROCESSES specifies the maximum number of
> operating system user processes that can simultaneously connect to Oracle.
> Its value should allow for all background processes such as locks, job
> queue processes, and parallel execution processes." (
> https://docs.oracle.com/cd/B19306_01/server.102/b14237/initparams169.htm#REFRN10175
> )
>
> Your system will choke before it gets anywhere close to this theoretical
> maximum. A rule of thumb is that you should be concerned if your db time
> exceeds elapsed time * CPU threads; that is, if average active sessions
> (AAS) is greater than the number of CPU threads (threads not cores).
>
> P.S. I hope that is not an interview question. I usually fail DBA
> interviews because of questions like that.
>
>
> https://iggyfernandez.wordpress.com/2010/10/31/the-worst-interview-of-my-life/
>
>
>
> https://iggyfernandez.wordpress.com/2012/07/16/how-not-to-interview-a-database-administrator-part-i-the-google-way/
>
>
>
>
>
>
>
>
> ------------------------------
> From: dba.tyagisumit_at_gmail.com
> Date: Sun, 22 May 2016 15:21:58 +0530
> Subject: DB TIME in AWR
> To: oracle-l_at_freelists.org
>
>
> *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? *
>
> Answer: Number of ‘sessions’ in int.ora * elapsed time = 300 * 1 hours =
> 300 Hours
>
> *OR *
>
> Answer : Number of ‘sessions’ in int.ora * elapsed time * CPU Cores =
> 300 * 1 * 4 = 1200 Hours
>
>
> Which one is correct any why . Little confusion here .
>
>
>
> --
>
> *--*
> *BR*
> *Sumit Tyagi*
> *+91-7829543355*
>
>
>
>
> --
>
> *--*
> *BR*
> *Sumit Tyagi*
> *+91-7829543355 <%2B91-7829543355>*
>

-- 

*--*
*BR*
*Sumit Tyagi*
*+91-7829543355*

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