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RE: Is nothing sacred? (Oracle vs The Experts)

From: Connor McDonald <hamcdc_at_yahoo.co.uk>
Date: Tue, 12 Nov 2002 15:40:30 -0800
Message-ID: <F001.005019DB.20021112154030@fatcity.com>


for a wonderful laugh download the TUSC (very recent) Oracle 9i performance tuning slides where there is a slide that is titled (something like)

"The 15% rule is back"

talking directly about amount of data returned via an index...

dear oh dear oh dear...

then there is also the "awesome" advice of "run queries regularly on your important indexes and tables to spike the sga with the data"

that is - do *more* work to get better performance

hello? hello? earth to tusc...come in..over

:-)

>
> An excellent example is the age old ideas that the
> earth was the center of
> the universe, that the world was flat, that the Cubs
> will never win another
> World Series (okay...bad example). Knowledge is
> limited by what we can
> currently test. We are always restricted by our
> physical world (I don't have
> a clue as to how I can personally test if the world
> is indeed round) but
> also by what we choose to accept as fact. What
> happens to indexing
> strategies when disk reads are faster than memory
> access operations? Before
> you say, "It will never happen" think about it...Can
> you predict the future
> with absolute certainty?
>
> Even the 'experts' choose to accept certain facts.
> Look at the scientific
> world. Many of the most 'brilliant' ideas now can be
> proven false. According
> to the experts, we only need 5 computers worldwide
> with 64k of memory.
>
> I checked by Data Server Internals texts from 1999
> and they preach 15% of
> rows returned for indexing, and this series is
> certainly looked upon as the
> 'expert'. Anyone out there with a more recent
> version? I wonder what it
> says...
>
> IMHO, the bottom line is that many of us are so
> concerned with just keeping
> systems running that we have no time for our own
> personal research and
> development. Until I decided to write an article
> about rollback segments, I
> never applied the scientific method to my
> understanding of Oracle. Will
> application of the method explain everything? Nope,
> but it will come close.
> It requires a lot of time and hard work, something
> that is a precious
> commodity these days, especially in the corporate
> world. I am very grateful
> for people like Cary, Tim, Anjo, Craig, Gaja, Kirti,
> et.al. who take the
> time to say "prove it!" and then perform the
> experiments and, most
> importantly, are willing to share the results with
> us on this list and at
> meetings like IOUG-A.
>
> Dan Fink
>
> -----Original Message-----
> Sent: Tuesday, November 12, 2002 2:24 PM
> To: Multiple recipients of list ORACLE-L
>
>
> I think the question "Is nothing sacred?" is an
> interesting one. Lots of
> these things we're talking about have been false for
> a very long time.
> It's only that people are finally starting to notice
> them. Product
> changes are often *not* what's driving "new
> knowledge." In many cases,
> the "change" that's taking place is the improvement
> in the quality of
> our conclusions.
>
> "Is nothing sacred?" I think it's perfectly
> legitimate to confront
> people's (and companies') conjectures with
> scientific data.
>
>
> Cary Millsap
> Hotsos Enterprises, Ltd.
> http://www.hotsos.com
>
> Upcoming events:
> - Hotsos Clinic, Dec 9-11 Honolulu
> - 2003 Hotsos Symposium on OracleR System
> Performance, Feb 9-12 Dallas
> - Jonathan Lewis' Optimising Oracle, Nov 19-21
> Dallas
>
>
> -----Original Message-----
> dgoulet_at_vicr.com
> Sent: Tuesday, November 12, 2002 10:19 AM
> To: Multiple recipients of list ORACLE-L
>
> Jesse,
>
> No, nothing in sacred any more. Change is the
> theme of the day.
> BTW: did
> you experiment with caching these tables in the
> keep_pool?? I've had
> some real
> good luck with unindexed tables that are small (in
> the 1 to 10 block
> size) that
> get assigned to the keep pool and retained in memory
> forever.
>
> Also, BTW: I'll disagree with Cary and Hotsos on
> the costs of a PIO
> vs a
> LIO. In my experience it's not such a clear cut
> distinction. Whenever
> Oracle
> needs a block of data that data must be in memory
> which means that a PIO
> requires 2 LIO's to fulfill the request and on top
> of that there may be
> other
> memory management routines that get called if an
> empty data block in
> memory must
> be created. All in all it's a very mixed bag that
> needs to be
> considered case
> by case. I believe that was one of the reasons
> Oracle allows us to
> configure
> the cache three ways. Static, seldomly changed
> tables in the keep pool.
> Large
> constantly changing tables in the discard pool.
> Also to index or not to
> index
> are no longer such clear cut item, especially with
> CBO which loves to
> ignore
> indexes.
>
> Dick Goulet
>
> ____________________Reply
> Separator____________________
> Author: "Jesse; Rich" <Rich.Jesse_at_qtiworld.com>
> Date: 11/11/2002 8:58 AM
>
> So, there I am, on 8.1.7.2 (and .4) on HP/UX 11.0,
> with a process that
> runs
> 20 minutes out of every hour of the day (despite my
> protests to it's
> design). After it starts having problems (go
> figure), it becomes a
> priority
> to speed it up.
>
> Thanks to a 10046 trace, we see that the query
> taking the most elapsed
> time
> does FTSs on each of two very small tables (1 block
> and 4 blocks -- 8K
> blocksize). These tables are not indexed, as per
> the official Oracle
> recommendation. After reading the excellent Hotsos
> paper "When to index
> a
> table" (THANKS, CARY!), I added an index to reduce
> elapsed time on this
> query by 50% (150 to 75 seconds in test), proving to
> me that the paper
> is
> valid. And I've only read to page four!
>
> OK, first I'm taught by Oracle to look at Buffer
> Cache Hit Ratios as a
> measure of performance, then told (and thoroughly
> convinced) by experts
> that
> this is bunk. Now, I found out that the 15% (or 10%
> or whatever,
> depending
> on version) ratio of rows returned to total rows in
> determining when to
> use
> an index in a query is garbage.
>
> 1) Why is this?
>
> 2) What other pearls of performance wisdom from
> Oracle Corp should I
> completely disregard as false?
>
> I know there's an Oracle Fallacy website
> somewhere...
>
> It just looks bad on me, our department, and Oracle
> when, once again,
> something I've been preaching to our developers as
> gospel turns out to
> be
> completely false.
>
> Maybe I'm grumpy because it's snowing on my leaves
> right now... <sigh>
>
>
> Rich
>
>
> Rich Jesse System/Database
> Administrator
> Rich.Jesse_at_qtiworld.com Quad/Tech
> International, Sussex, WI
> USA
>
> Disclaimer: I only said the Packers would be 12-4
> this year -- I never
> said
> that they couldn't do better! WOO-HOO! :)
> --
> Please see the official ORACLE-L FAQ:
> http://www.orafaq.com
> --
> Author: Jesse, Rich
> INET: Rich.Jesse_at_qtiworld.com
>
> Fat City Network Services -- 858-538-5051
> http://www.fatcity.com
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>



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Connor McDonald
http://www.oracledba.co.uk
http://www.oaktable.net

"GIVE a man a fish and he will eat for a day. But TEACH him how to fish, and...he will sit in a boat and drink beer all day"



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Received on Tue Nov 12 2002 - 17:40:30 CST

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