Hmm, parsing is not done at the open (oopen call). It is done in the
oparse/osql call. But they are deffered until the execute. So it looks like
it is done at the execute. In OCI8 it is a different story all together.
Anjo.
- Original Message -----
To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com>
Sent: Thursday, July 25, 2002 6:59 PM
> Possibly burying myself deeper: Parsing is done at the open call. If a
cursor needs to be
> re-opened, Oracle will check for permissions whether cursors are cached or
not.
>
> Some experiments. First just using bind variables in the statement.
>
> SQL> alter session set session_cached_cursors = 10;
>
> Session altered.
>
> SQL> VARIABLE V_EMPNO NUMBER
>
> BEGIN
> :V_EMPNO := 7934;
> END;
> /
> SQL> select ename from scott.emp where empno = :v_empno;
>
> ENAME
> ----------
> MILL
>
> As this is the first statement. I would expect hard and soft parsing to
be taking place.
>
> SQL> BEGIN
> 2 :V_EMPNO := 7782;
> 3 END;
> 4 /
>
> PL/SQL procedure successfully completed.
>
> SQL> select ename from scott.emp where empno = :v_empno;
>
> ENAME
> ----------
> CLARK
>
> What type of parsing is done here. The statement is in the buffer pool
>
> --------------------------------------------------------------------------
> If "scott" revokes privileges
>
> and the above statement is rerun
>
> SQL> /
> select ename from scott.emp where empno = :v_empno
> *
> ERROR at line 1:
> ORA-01031: insufficient privileges
> --------------------------------------------------------------------------
> Scott restores privileges ...
>
> SQL> variable my_select refcursor;
> SQL> BEGIN
> 2 OPEN :my_select FOR SELECT ename from s
> 3 END;
> 4 /
>
> PL/SQL procedure successfully completed.
>
> SQL> print my_select
>
> ENAME
> ----------
> SMITH
> ALLEN
> WARD
> JONES
> MARTIN
> BLAKE
> SCOTT
> KING
> TURNER
> ADAMS
> JAMES
> FORD
> MILL
> CLARK
>
> 14 rows selected.
> --------------------------------------------------------------------------
> Print closes the cursor.
>
> If "scott" revokes permisssions at this point.
>
> SQL> BEGIN
> 2 OPEN :my_select FOR SELECT ename from scott.emp;
> 3 END;
> 4 /
> OPEN :my_select FOR SELECT ename from scott.emp;
> *
> ERROR at line 2:
> ORA-06550: line 2, column 45:
> PLS-00904: insufficient privilege to access object SCOTT.EMP
> ORA-06550: line 2, column 21:
> PL/SQL: SQL Statement ignored
> --------------------------------------------------------------------------
> However if scott restores permissions
>
> SQL> BEGIN
> 2 OPEN :my_select FOR SELECT ename from scott.emp;
> 3 END;
> 4 /
>
> PL/SQL procedure successfully completed.
>
> and now revokes them here.
>
> The print statement will still work
>
> SQL> print my_sele
>
> ENAME
> ----------
> SMITH
> ALLEN
> WARD
> JONES
> MARTIN
> BLAKE
> SCOTT
> KING
> TURNER
> ADAMS
> JAMES
> FORD
> MILL
> CLARK
>
> 14 rows selected.
> --------------------------------------------------------------------------
> So how does one keep such cursors open. Given a cursor such as
>
> BEGIN
> OPEN :my_select FOR SELECT ename from scott.emp
> where empno = :v_empno;
> END;
>
> How does one display the information, change the value of :v_empno, and
display the infromation again without re-opening the cursor.
>
> In the distant past when I was writing a lot of Pro*C I'd get the
occaisional fetch out of sequence error when I would change the value of a
bind variable and try to fetch without first opening the cursor. Doesn't
one have to re-opne to rebind.
>
> N.B. mail sent in haste -- late for an appointment.
>
> Ian MacGregor
> Stanford Linear Accelerator Center
> ian_at_SLAC.Stanford.edu
>
>
>
>
>
>
>
>
> -----Original Message-----
> Sent: Thursday, July 25, 2002 12:38 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
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> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.com
> --
> Author: Jared Still
> INET: jkstill_at_cybcon.com
>
> Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051
> San Diego, California -- Public Internet access / Mailing Lists
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> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.com
> --
> Author: MacGregor, Ian A.
> INET: ian_at_SLAC.Stanford.EDU
>
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--
Please see the official ORACLE-L FAQ: http://www.orafaq.com
--
Author: Anjo Kolk
INET: anjo_at_oraperf.com
Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051
San Diego, California -- Public Internet access / Mailing Lists
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Received on Fri Jul 26 2002 - 15:48:43 CDT
