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Home -> Community -> Mailing Lists -> Oracle-L -> RE: Is nothing sacred? (Oracle vs The Experts)
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.
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, WIUSA Disclaimer: I only said the Packers would be 12-4 this year -- I never said
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--
Please see the official ORACLE-L FAQ: http://www.orafaq.com
--
Author: Cary Millsap
INET: cary.millsap_at_hotsos.com
Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services ---------------------------------------------------------------------To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing). Received on Tue Nov 12 2002 - 15:23:53 CST
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