Re: i/o parameters on oracle and sun

"Spencer" <spencerp_at_swbell.net> wrote in message news:i0P96.5432$hD5.87989_at_nnrp1.sbc.net...
> jonathon and connor have both already hit the (proverbial)
> nail on the head. and, at a risk of delivering a glancing
> blow and bending it over sideways... here's my swing at it
>
> assuming an oracle block size of 4K
>

...which is a very bad size for an Oracle block, given that Oracle block sizes should be determined solely by the operating system you are using, if you know what's good for you (and see www.ixora.com.au if you are not convinced)......

> the odds that a single multiblock read of 16 blocks (64K)
> will require i/o operation on more than one device are:
>
> 1 in 2 given a stripe size of 128K
> 15 in 16 given a stripe size of 64K
> 1 in 1 given a stripe size of 32K
>
> the odds that a single multiblock read of 8 blocks (32K)
> will require i/o operations on more than one device are:
>
> 1 in 4 given a stripe size of 128K
> 1 in 2 given a stripe size of 64K
> 7 in 8 given a stripe size of 32K
>
> the odds that a single multiblock read will require more
> than one i/o operation on a single device are:
>
> 1 in 1 if request size > stripe size * no.of disks
> 0 if request size <= stripe size * no.of disks
>
> the odds that multiple i/o operations against a single
> device will be combined together into a single larger
> i/o operation (e.g. by async or list io) are:
>
> dependent on factors in addition to stripe size.
>
> the odds that a block will already be in the buffer cache
> and not require any i/o operation are:
>
> dependent on factors other than stripe size.
>
> does anyone care to place a wager ?
>
> "Jonathan Lewis" <jonathan_at_jlcomp.demon.co.uk> wrote in message
> news:979814882.27443.0.nnrp-02.9e984b29_at_news.demon.co.uk...
> >
> > More particularly, you do not want a single multiblock read
> > to be larger than the amount of data that can be found on a
> > single disk (unless the system is a single user system) otherwise
> > a single Oracle read request ends up queuing and blocking on more
> > than one device.
> >
> > --
> > Jonathan Lewis
> > Yet another Oracle-related web site: http://www.jlcomp.demon.co.uk
> >
> > Practical Oracle 8i: Building Efficient Databases
> >
> > Publishers: Addison-Wesley
> > See a first review at:
> > http://www.ixora.com.au/resources/index.htm#practical_8i
> > More reviews at: http://www.jlcomp.demon.co.uk/book_rev.html
> >
> > Connor McDonald wrote in message <3A643625.979_at_yahoo.com>...
> > >thus smaller stripe sizes could perform better - but as you said, you
> > >would not want a single multblock read to be larger than no. disks *
> > >stripe size since you would get nasty 'wraparound'.
> > >
> >
>
>
>
Received on Fri Jan 19 2001 - 08:33:03 CST