RE: Detecting xxx fragmentation/corruption?

You can find Cary Millsap's paper,

                                                Why You Should Focus on LIOs Instead of PIOs

at http://www.hotsos.com/library.html

peter

> Date: Sun, 11 May 2008 22:38:17 +0800
> From: htmldeveloper_at_gmail.com
> To: daniel.fink_at_optimaldba.com
> Subject: Re: Detecting xxx fragmentation/corruption?
> CC: oracle-l_at_freelists.org
>
> On Sat, May 10, 2008 at 9:55 AM, Daniel Fink <daniel.fink_at_optimaldba.com> wrote:
> > To supplement Jared's response... Inline
> >
> >
> > Peter Teoh wrote:
> >>
> >> Unlike memory, where access time almost zero, accessing the disk is
> >> much slower. So sometimes I thought it will be better to spread out
> >> the data - thus enable simultaneous read by the different heads in the
> >> disk, just like those RAID design. Ie, fragmentation via
> >> distribution the blocks out in the disk can improve performance - can
> >> such things happened?
> >>
> >
> > In terms of reading data in memory, access time may be almost zero, but the
> > time required to read a block in memory is not thousands of times faster
> > than reading it from disk. I don't recall the exact figure from a Cary
> > Millsap presentation ("Why You Should Focus on LIOs"?)some years ago, but
> > the difference was something like 42 times. If you add in time required to
> > create a read consistent version, a single logical i/o could take much more
> > time than a physical i/o.
>
> I have yet to find Cary Millsap article, but this (by Don Burleson) is
> interesting:
>
> http://www.dba-oracle.com/oracle_tips_high_lio.htm
>
> One of the issues is the relatively high-cost of fetching an Oracle
> data block from disk. In theory RAM is 10,000 times faster than disk
> milliseconds vs. nanoseconds), but when you add-in the overhead of
> lock serialization and latches, a logical I/O might be less than a
> thousand times faster than a "physical" disk I/O.
>
> And this one from AskTom specifically on LIO is interesting:
>
> http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:6643159615303
> >
>
> > --
> > Daniel Fink
> >
>
> In general...I do agree that LIO involves lots of transaction
> handling, and CPU crunching...esp with Oracle read-consistency
> requirements.
>
> Thanks.
>
> --
> Regards,
> Peter Teoh
> --
> http://www.freelists.org/webpage/oracle-l
>
>

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