Connor,
Well, technically that answers the "why"... with Oracle's "because I
said so" :)
the REAL question is why 3 and not 2 or 4 or 10 or..... ?
Rachel
- Connor McDonald <hamcdc_at_yahoo.co.uk> wrote:
> "RTM" :-)
>
> Performance Guide 9.2
>
> "Caching Session Cursors
>
> (blah blah blah)
>
> Oracle checks the library cache to determine whether
> more than three parse requests have been issued on a
> given statement.
>
> (more blah blah blah)"
>
> hth
> connor
>
>
> --- Jared.Still_at_radisys.com wrote: > I wasn't aware
> of it requiring three calls before
> > being useful.
> >
> > Why is that?
> >
> > Jared
> >
> >
> >
> >
> >
> > "Cary Millsap" <cary.millsap_at_hotsos.com>
> > Sent by: root_at_fatcity.com
> > 07/25/2002 07:58 AM
> > Please respond to ORACLE-L
> >
> >
> > To: Multiple recipients of list ORACLE-L
> > <ORACLE-L_at_fatcity.com>
> > cc:
> > Subject: RE: Cursor Sharing| Soft
> > Parsing
> >
> >
> > Well, three times, right? I think it takes three
> > parse calls before
> > session_cached_cursors begins to help. But 3 is
> > still O(1). Once per
> > call is O(#executions).
> >
> >
> > Cary Millsap
> > Hotsos Enterprises, Ltd.
> > http://www.hotsos.com
> >
> > Upcoming events:
> > - Hotsos Clinic, Jul 23-25 Chicago
> > - Miracle Database Forum, Sep 20-22 Middlefart
> > Denmark
> > - 2003 Hotsos Symposium on OracleR System
> > Performance, Feb 9-12 Dallas
> >
> >
> >
> > -----Original Message-----
> > Still
> > Sent: Thursday, July 25, 2002 2:38 AM
> > To: Multiple recipients of list ORACLE-L
> >
> > On Wednesday 24 July 2002 22:08, MacGregor, Ian A.
> > wrote:
> > > Please define soft parsing. Oracle needs to check
> > that the user
> > > submitting a SQL statement has permissions to run
> > it. It has to do
> > this
> > > every time a statement is run, bind variables or
> > not.
> >
> > No, code that uses bind variables need only parse
> > SQL statements
> > once if session_cached_cursors is set. Further
> > executions of the same
> > SQL don't require a hard or soft parse.
> >
> > Jared
> >
> > > When "cursor-sharing" converts a statement to use
> > bind variables it
> > would
> > > save on hard parsing, if a match were found the
> > pool; also, it could
> > lessen
> > > the number of statements present in the pool.
> > >
> > > Ian MacGregor
> > > Stanford Linear Accelerator Center
> > > ian_at_SLAC.Stanford.edu
> > >
> > > -----Original Message-----
> > > Sent: Wednesday, July 24, 2002 9:23 PM
> > > To: Multiple recipients of list ORACLE-L
> > >
> > >
> > > Mike, Kirti,
> > >
> > > Try page 441
> > >
> > > CURSOR_SHARING=FORCE does improve badly written
> > applications that use
> > lots
> > > of literals.
> > > However coding should be done using bind variables
> > in almost all
> > occasions.
> > >
> > > CURSOR_SHARING=FORCE reduces the hard parsing.
> > >
> > > What CURSOR_SHARING=FORCE does is rewrites all
> > queries to use bind
> > > variables before parsing.
> > >
> > > eg. select ename from emp where empno = 10;
> > > rewritten as
> > > select ename from emp where empno =:SYS_B_0
> > > or in 8.1.6 , 8.1.7
> > > select name from emp where empno =:"SYS_B_0"
> > >
> > > So it substitutes the literal with bind variables
> > but incurs the cost
> > of
> > > soft parsing the statement.
> > > Soft Parsing too frequently limits the scalability
> > of applications and
> > > sacrifices optimal performance which could have
> > been achieved in the
> > first
> > > place if written using bind variables.
> > >
> > > Parse once and execute as many times as we like.
> > >
> > > Also check out Bjorn's paper on bind variables and
> > cursor sharing at
> > >
> >
> http://technet.oracle.com/deploy/performance/pdf/cursor.pdf
> > >
> > > So CURSOR sharing is not the "silver bullet" as
> > one may expect.
> > >
> > > Regards
> > > Suhen
> > >
> > > On Thu, 25 Jul 2002 10:23, you wrote:
> > > > Mike,
> > > > What is the version of the database? Some
> > versions of 8.1.7 had a
> > few
> > > > bugs when this parameter was set to FORCE. I
> > suggest searching
> > Metalink.
> > > > But it does work as advertised in later
> > releases. I would also
> > recommend
> > > > reviewing Tom Kytes' book to read about his
> > views in using this
> > parameter
> > > > at the instance level (my boss is reading my
> > copy, so I can't give
> > you
> > > > page #s).
> > > >
> > > > - Kirti
> > > >
> > > > -----Original Message-----
> > > > Sent: Wednesday, July 24, 2002 6:08 PM
> > > > To: Multiple recipients of list ORACLE-L
> > > >
> > > >
> > > > Has anyone set Cursor Sharing to Force ?
> > > > I have a new system that we have to support
> > > > and there is alot literals filling up the
> > > > pool. I have never changed this parameter
> > > > from the default as many seemed to think the
> > > > jury was still out on it. However, due to
> > > > my situation, I figured I would try it out.
> > > > If anyone has any experience with this one
> > > > I would be curious to know what happened.
> > > >
> > > > Mike
> > >
> > > --
> > > Please see the official ORACLE-L FAQ:
> > http://www.orafaq.com
> > > --
> > > Author: Suhen Pather
> > > INET: Suhen.Pather_at_strandbags.com.au
> > >
> > > Fat City Network Services -- (858) 538-5051
> > FAX: (858) 538-5051
> > > San Diego, California -- Public Internet
> > access / Mailing Lists
>
=== message truncated ===
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--
Please see the official ORACLE-L FAQ: http://www.orafaq.com
--
Author: Rachel Carmichael
INET: wisernet100_at_yahoo.com
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Received on Fri Jul 26 2002 - 08:28:26 CDT
