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
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
[EMAIL PROTECTED] 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! :)
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