Re: Cursor Sharing| Soft Parsing

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
>
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Author: Jared Still
  INET: jkstill_at_cybcon.com

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