Oracle-L: RE: cursor_sharing in 8.1.7.4

From: Cary Millsap <cary.millsap_at_hotsos.com>
Date: Tue, 19 Aug 2003 20:59:24 -0800
Message-ID: <F001.005CB9FE.20030819205924@fatcity.com>

And don't count too heavily upon 9i's "bind value peek" capability. Here's a simple test that Jonathan Lewis conjured up last year:

PREPARATION. Create data for "select c1, c2 from t1 where c1 = :bind1", where different bind1 values could have different paths if we used literals.

flush shared pool set bind1 = 5 execute query, notice an indexed access (optimal plan for bind1=5) set bind1 = 70 execute query, notice that kernel still uses the index
flush shared pool set bind1 = 70 execute query, notice a table scan (optimal plan for bind1=70) set bind1 = 5 execute query, notice that kernel still uses the table scan

The moral: the kernel only peeks once per session.

Cary Millsap
Hotsos Enterprises, Ltd.
http://www.hotsos.com

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-----Original Message-----
Jesse, Rich
Sent: Tuesday, August 19, 2003 3:09 PM
To: Multiple recipients of list ORACLE-L

True, but using binds isn't always an option, like when running a 3rd party
product. I also could not justify weeks of recoding homegrown software for
the relatively minor gains we would have using binds. And scalability (or
lack thereof) didn't seem to be argument enough.

We're using CS=F on 8.1.7.4 on HP/UX 11.0. We haven't yet had a single issue attributable to it in the 7 months we've been at the .4 release. There were some nasty issues with 8.1.7.2 (ORA-600 and silently returning
WRONG data), but like I said, .4 seems to have cleaned that up. YMMV.

Remember that under 8i, you may see some performance DROP by using binds.
The case that comes to mind is if you're using histograms with ANALYZE or
DBMS_STATS. Under 8i, the optimizer can no longer "see" the values and therefore can't use the histograms. Under 9i (R2 only?), you can tell the
optimizer to peek at the bind variables' values in order to make use of histograms. We plan on doing this when we get to 9i in order to use a very
low cardinality index, where less than 0.0001% of the rows is what we need
to fetch, but 8i won't use the index because of the cardinality.

Your best bet, of course, is to test! HTH! GL! :)

Rich

Rich Jesse                           System/Database Administrator
rjesse_at_qtiworld.com                  Quad/Tech Inc, Sussex, WI USA

-----Original Message-----
Sent: Tuesday, August 19, 2003 2:49 PM
To: Multiple recipients of list ORACLE-L

Hi,
No. I recommend that you do not change cursor_sharing if you are doing it
just to get rid of 4031. There could be serious problems. ora-600 etc. Maybe
Oracle has fixed everything in latest 817 but I suggest not to take that chance.
For 4031 you can do the following : pin pl/sql sql preferably at startup,
use bind variables and periodically check for sql not using bind variables.
Goodluck.

"Fedock, John (KAM.RHQ)" <John.Fedock_at_us.kline.com> wrote:

Does anyone have any experience using cursor_sharing in 8.1.7.4? I feel I
need to use it due to literal SQL statements being used. We have had misc
4031 errors off and on and I feel this is my last hope. I have a very busy
OPFS server (HP-UX).

I did try using cursor_sharing in 8.1.7.2, and I remember incorrect sorting
and other unexpected results happening.

Thanks for any input.

John
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Author: Jesse, Rich
INET: Rich.Jesse_at_qtiworld.com

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Author: Cary Millsap
INET: cary.millsap_at_hotsos.com

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RE: cursor_sharing in 8.1.7.4 - good or bad