Mark, I saw and read the thread and I've read the paper.
Dan was talking about how in '99 Oracle was preaching 15% and I told what I had been told, by Oracle in 2000. Two years makes an awfully large difference in what the party line is and becomes. And I also said that I don't follow that as a rule, but work off performance and the explain plan. If the performance dies with an index usage and improves without it, I make sure the index isn't used FOR THAT QUERY. Rachel --- "Mark J. Bobak" <[EMAIL PROTECTED]> wrote: > Rachel, > > In case you missed the mention earlier in the thread, go to > http://www.hotsos.com/ and click the "Knowledge On-line" link and > look > for a paper called "When to use an index". Cary does an excellent > job > explaining why row selectivity is a totally invalid criteria. He > then > proceeds to demonstrate how index access may be valid for 100% > selectivity, and how FTS access may be valid for 1% or less > selectivity. > > If you haven't seen it, it's a great read. > > -Mark > On Tue, 2002-11-12 at 19:48, Rachel Carmichael wrote: > > last time I checked with an Oracle University instructor who I > trust as > > knowledgeable, it was FTS if more than 5-8% of rows expected to be > > returned. This was 2000. These days, who knows? > > > > I don't go by the rules much anymore but by perception of > performance > > and by explain plan analysis. > > > > > > --- "Fink, Dan" <[EMAIL PROTECTED]> wrote: > > > Of course, sacred cows make the best steaks (sorry, Gaja). > > > > > > 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----- > > > [EMAIL PROTECTED] > > > 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" <[EMAIL PROTECTED]> > > > 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 > === message truncated === __________________________________________________ Do you Yahoo!? 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