# Re: Queueing Theory in Oracle

From: Marcin Przepiorowski <pioro1_at_gmail.com>
Date: Tue, 25 Mar 2014 19:22:41 +0000

Hello All,

I did some work using QT and Oracle in 2002 or 2003 (just 2 - 3 years after I finished college).
At that time I was brave enough to starting building a queuing model of major Oracle components
- of course if was very complex and even simulation tools I used for it was unable to give me results close to my expectation. Thankfully I read Cary's book and early Craig papers about it and decide that simple M/M/n should work for 90 % of capacity planing exercises.

As Andrey mentioned above we can use G/G/n instead of M/M/n but it will be more complex.

In terms of exponentiation arrival rate I think is more important to be use that metric that we will use will be independent and identically distributed.

Probably title of the book is not a best one for science brains but I would recommend to read this book if you are interested in modeling system - "The art of computer system performance analysis" by Raj Jain - http://www.amazon.com/The-Computer-Systems-Performance-Analysis/dp/0471503363 - not a newest one but math is math.

regards,

```--
Marcin Przepiorowski
http://oracleprof.blogspot.com

On Sun, Mar 16, 2014 at 3:51 PM, Николаев Андрей Серапионович <
Andrey.Nikolaev_at_rdtex.ru> wrote:

> Hello!
> >I am asking if anyone has successfully used queuing theory in Oracle ...
>
> This is very interesting and still developing research area. Typically,
> the Oracle database internal algorithms are much more complex then the
> standard QT models.
>
> In my opinion, the QT provides us with phenomenological background about
> the observables (utilization, arrival rate, queue length, wait time,
> service demand ...) and their interdependences (Little's Law, (1-u)^-1
> behavior,  ...)
>
> This result in the phenomenological rules such as: Amdahl's law, Universal
> Scaling law by Neil Gunther, "Magic of 2" by Cary Millsap, ...
> All the above allows the performance capacity planning and predicting.
>
> In addition to previously discussed in this thread the classical books by
> Cary Millsap,  Craig Shallahammer, and the Hotsos presentations by Henry
> Poras, I would like to recommend the inspiring books by Dr. Neil Gunther.
>
>
> >I guess to use M/M/n we just have to assume certain database metrics are
> >exponentially distributed such as ...
> >If not we arent suppose to use queueing theory because it is based on
> >exponentially distributed data.
>
> Unless you encounter a heavy tailed distribution, the Law of large numbers
> Approximate G/G/n formulas show behaviors close to the corresponding M/M/n
> formulas and generally differ only by multipliers.
> Therefore, you can use M/M/n expressions for estimations.
>
> However, Dr. Neil Gunther at Hotsos 2012 demonstrated that the heavy
> tailed distributions and the "fractal behavior" do exist in Oracle world.
> Such cases require more complicated treatment.
>
> >Maybe some wait events about latches/mutex/... can be seen as pure
> QueueTime...
>
> Despite the classical QT works well for estimations, the detailed
> investigation of the queuing properties for even the simplest Oracle
> objects, such as mutexes is more complicated.
>
> For example, the "wait" in Oracle has the different meaning then wait in
> Queuing Theory. Even the "average wait time" has another definition.
>
> Some time ago, I presented about Oracle mutexes and the corresponding
> queuing models.
> If you are interesting, you can find the article at
> http://arxiv.org/abs/1212.6640
>
> With Best Regards
> Andrey Nikolaev
> http://andreynikolaev.wordpress.com
>
>
> --
> http://www.freelists.org/webpage/oracle-l
>
>
>

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```
Received on Tue Mar 25 2014 - 20:22:41 CET

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