Thanks for the clarifications, Cary.
With regards to a hardware sizing - how do LIOs fit
into queueing theory? Let's say I can come up with
something like:
#CPUs required = Sum( LIOs(Bus.Tx i)) /
(10,000*clock rate/100)
where i={Bus.Tx 1..n}
[on a projected box that haven't been bought yet, it
might be a little difficult to estimate the
denominator, ... and on the existing one I guess I
have to get hold of Jonathan's paper to learn how this
can be done]
..but in any event for forecasting purposes, how
queueing effect might be taken into account here?
Let's say I measured Sum( LIOs(...)) for a 50 users in
a unit testing environment and I am told that
production would be 10 times more than that, what do I
do?
Thanks,
Boris Dali.
- Cary Millsap <cary.millsap_at_hotsos.com> wrote: >
My answers are in-line, preceded with “[Cary
> Millsap]”...
>
>
> Cary Millsap
> Hotsos Enterprises, Ltd.
> http://www.hotsos.com
>
> Upcoming events:
> - Performance Diagnosis 101: 12/16 Detroit, 1/27
> Atlanta
> - SQL Optimization 101: 12/8 Dallas, 2/16 Dallas
> - Hotsos Symposium 2004: March 7-10 Dallas
> - Visit www.hotsos.com for schedule details...
>
>
> -----Original Message-----
> Boris Dali
> Sent: Sunday, December 07, 2003 9:54 AM
> To: Multiple recipients of list ORACLE-L
>
> Thanks a lot for the reply, Cary. Yes, your
> explanation makes all the sense in the world even
> though it is precisely the weighted average approach
> that I've seen on some capacity planning
> spreadsheets.
>
> Two additional questions if I may, Cary.
> Would it be correct to say that when I throw
> additional users on a system it is only queueing
> component of a response time that climbs up, while
> service time stays the same?
>
> [Cary Millsap] “Sort of,” but not exactly. There are
> lots of scalability
> threats that begin to manifest in reality when you
> crank up the load.
> For example, you’ll see “latch free” waiting on
> applications that parse
> too much, but only at higher user volumes (never in
> unit test). You can
> consider the new appearance of “latch free” events
> to be a type of
> queueing if you want, but it’s really not queueing
> in the sense of a
> simple CPU queueing model.
>
> If that's true, than does
> it matter how I measure service time of my Bus.Tx1 -
> on a loaded system where hundreds of users run this
> operation or when nobody executes it all? Also is it
> important to have the other two operations - Bus.Tx2
> and Bus.Tx3 - running concurrently (as they would in
> a
> real life) for the c measurements?
>
> [Cary Millsap] You’ll put yourself at risk if you
> simply try to use a
> queueing model to extrapolate big-system performance
> from data collected
> in a unit testing environment. It’s because of the
> potentially
> out-of-model scalability threats.
>
> In other words assuming I have an identical replica
> of
> a production environment where I am the only user -
> would service time/rate measured there be applicable
> for a loaded system with heterogeneous workload?
>
> [Cary Millsap] ...Only if you your production
> environment doesn’t
> trigger any new serialization issues that weren’t
> visible on your unit
> test env.
>
> And another stupid question.
> Knowing individual business tx. characteristics
> (response time, number of CPUs required to comply
> with
> SLA requirements, average utilization per CPU, etc),
> how does one go about sizing the box in terms of the
> overall "system" required CPU capacity? Or put it
> another way - what do I tell a hardware vendor?
>
> That is, if what comes out of a queueuing exercise
> is:
> m pho
> -------- ---
> Bus.Tx1 2-way 70%
> Bus.Tx2 3-way 50%
> Bus.Tx3 4-way 80%
>
> What should be the optimistic (let's assume perfect
> liner CPU scalability for now) recommendation to
> decision makers in terms of the horsepower required
> to
> run this "system" on?
> After all, yes individual business transactions have
> their own SLA requirements (e.g. worst tolerated
> response time), but they all use the same resources,
> don't they? So even though a service time of Bus.Tx1
> might remain constant the queueing delay (and hence
> the response time) would likely to increase due to
> other concurrent activities on the system. Is there
> a
> way to account for this if capacity planning is done
> at the individual bus.tx level?
>
> [Cary Millsap] The hardest part about capacity
> planning is that there’s
> no useful industry-wide standard unit of CPU work to
> use. You can’t use
> MHz, you can’t use MIPS, and you can’t use SPECints,
> or anything else
> like that. But you can use Oracle LIOs. It’s not
> hard to test a system
> to see how many LIOs/sec it can handle; this is your
> supply (capacity).
> It’s also not hard to see how many LIOs/sec an
> application needs; this
> is your demand (workload). With this realization,
> capacity planning is
> much simpler. The game is to ensure that supply
> exceeds demand at all
> times, and by a sufficient amount so that you don’t
> have unstable
> response times.
>
> [Cary Millsap] ...And, of course, as I mentioned
> previously, you have to
> keep your peripheral vision open for the possibility
> that some new
> scalability threat will manifest and surprise you.
>
>
> Thanks,
> Boris Dali.
=== message truncated ===
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Received on Sun Dec 07 2003 - 12:39:24 CST
