Re: Number of IOs Per Second

CHANGE USERNAME TO westes wrote:
>
> "Connor McDonald" <connor_mcdonald_at_yahoo.com> wrote in message
> news:411A1C97.7D97_at_yahoo.com...
> > CHANGE USERNAME TO westes wrote:
> > Your queries won't generate "IOs per sec", they will simply generate
> > "IO". You could imagine a worst case scenario would be a nested loop
> > cartesian join (8m x 8m x size of table A x size of table B). eg 200
> > bytes per table yields around 2 terabytes of disk read. Hopefully your
> > queries will be better than that :-)
> >
> > Once you've got a handle on typical IO, and how long the queries are
> > allowed to take, *then* work out what IO's per second you need to
> > achieve the results you need.
>
> That's very clear thinking, and your example for calculation of amount of
> data is helpful.
>
> What should I be using as a figure for the amount of data in each I/O? I
> am referring to disk-level I/O and not OS-level I/O, since I have as one
> data point that a single physical disk will give me something around 100
> disk-level IOs per second.
>
> So in your scheme, I am left with a formula to calculate the number of disks
> I need based on amount of data I collect and time I need to collect it.
>
> # of disks = Y GB per data collection / [ 100 IOs per disk per second *
> .000256 GB per IO (or whatever the physical IO size is) * Y Desired Seconds
> per data collection ]
>
> Is this the basic idea?
>
> --
> Will
> westes AT earthbroadcast.com

That a sound starting point.. If your system already exists, then its relatively easy to determine the IO's that key queries will require - you simply trace them and check the physical reads performed.

If the system is "vapourware" then of course its a little tougher...

hth

-- 
Connor McDonald
Co-author: "Mastering Oracle PL/SQL - Practical Solutions"
ISBN: 1590592174

web: http://www.oracledba.co.uk
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email: connor_mcdonald_at_yahoo.com

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