Re: Library Cache

On Dec 30, 9:01 am, mrdjmag..._at_aol.com wrote:
> On Dec 29, 12:14 pm, ddf <orat..._at_msn.com> wrote:
>
>
>
>
>
> > On Dec 29, 11:10 am, mrdjmag..._at_aol.com wrote:
>
> > > On Dec 29, 11:03 am, "gym dot scuba dot kennedy at gmail"
>
> > > <kenned..._at_verizon.net> wrote:
> > > > <mrdjmag..._at_aol.com> wrote in message
>
> > > >news:3e0d392e-2c18-4ad2-b9d2-36273b652062_at_q30g2000prq.googlegroups.com...
> > > > On Dec 29, 9:09 am, Mark D Powell <Mark.Pow..._at_eds.com> wrote:
>
> > > > > On Dec 29, 9:53 am, mrdjmag..._at_aol.com wrote:
>
> > > > > > Hi,
>
> > > > > > We installed this Spotlight for Oracle software. The software shows
> > > > > > an 85% re-parse rate against the Library Cache. Here is the biggest
> > > > > > issue we have. I do not think anything can be done, but maybe another
> > > > > > brain can figure something out:
>
> > > > > > We have a table with stored queries:
> > > > > > Row 1: SELECT emp_num FROM employees
> > > > > > Row 2: SELECT address FROM customer_address
>
> > > > > > We have a criteria table which holds any criteria that the query MAY
> > > > > > use:
> > > > > > Row 1: WHERE emp_first =
> > > > > > Row 1: AND emp_last =
> > > > > > Row 2: WHERE customer_id =
>
> > > > > > So, the PHP code can pass any number of parameters to the procedure,
> > > > > > which the procedure can parse and form the query and open a cursor for
> > > > > > the PHP code to read.
>
> > > > > > This means that the queries may/may not be the same, and need to be re-
> > > > > > parsed. So, we lose on that. Is there anything that can be done to
> > > > > > tune these and make them faster? An index against every possible
> > > > > > combination is not possible, and we have hundreds of these stored
> > > > > > queries........
>
> > > > > > Any smarter people have any ideas?
>
> > > > > > Arthur
>
> > > > > If the SQL built from the logic includes constants for the where
> > > > > clause conditions you could change it to use bind variables in the
> > > > > code. This would give you some reuse.
>
> > > > > You could replace the SQL in tables with SQL housed in stored
> > > > > procedures that determines the SQL to be submitted based on the
> > > > > parameters passed in. These statements would all use bind variables.
> > > > > The procedures could pass cursors back to the application.
>
> > > > > Take a look at the value of your database parameter cursor_sharing.
> > > > > The default is EXACT. You might be able to get some benefit from
> > > > > changing it to SIMILAR or FORCE. SQL plan changes are possible if
> > > > > this parameter is changed so some tuning may be required.
>
> > > > > HTH -- Mark D Powell --
>
> > > > Mark,
>
> > > > How about a query done like this:
>
> > > >    v_optin_str :=  'SELECT COUNT(*) FROM email_list a
> > > >                     WHERE '||v_date_clause||' '||v_adid_clause||
> > > >                           ' AND customer_id IS NOT NULL
> > > >                             AND adid IS NOT NULL
> > > >                             AND EXISTS (SELECT user_session
> > > >                                         FROM EMAIL_ALERTS b
> > > >                                         WHERE alert_type = ''OI''
> > > >                                         AND b.user_session =
> > > > a.user_session)';
>
> > > >    EXECUTE IMMEDIATE v_optin_str
> > > >    INTO stats_tab(199)
> > > >    USING p_b_date, p_e_date;
>
> > > > Is that correctly using the bind variables?
>
> > > > Ugly, very ugly.  No that isn't using bind variables.  You need
> > > > :bind_variable_name.
>
> > > Yeah, we had some seriously shit programmers........time for an ALL
> > > STORED PROCEDURE fix.
>
> > > Basically where ever there is dynamic SQL, it can be replaced by bind
> > > variables.
>
> > > Just curious, what is the real difference between using "v_variable"
> > > and "USING :v_variable" if the values get replaced?- Hide quoted text -
>
> > > - Show quoted text -
>
> > One becomes a string literal and one does not:
>
> > SQL> create or replace procedure nobind_example(p_var in varchar2)
> >   2  is
> >   3          v_sqlstr varchar2(2000);
> >   4          v_rec_ct number;
> >   5
> >   6  begin
> >   7          v_sqlstr:='select count(*) from emp where ename = '''||
> > p_var||'''';
> >   8
> >   9          dbms_output.put_line(v_sqlstr);
> >  10
> >  11          execute immediate v_sqlstr
> >  12          into v_rec_ct;
> >  13
> >  14          dbms_output.put_line(v_rec_ct);
> >  15
> >  16  end;
> >  17  /
>
> > Procedure created.
>
> > SQL>
> > SQL> create or replace procedure bind_example(p_var in varchar2)
> >   2  is
> >   3          v_sqlstr varchar2(2000);
> >   4          v_rec_ct number;
> >   5
> >   6  begin
> >   7          v_sqlstr:='select count(*) from emp where ename = :1';
> >   8
> >   9          dbms_output.put_line(v_sqlstr);
> >  10
> >  11          execute immediate v_sqlstr
> >  12          into v_rec_ct
> >  13          using p_var;
> >  14
> >  15          dbms_output.put_line(v_rec_ct);
> >  16
> >  17  end;
> >  18  /
>
> > Procedure created.
>
> > SQL>
> > SQL> set serveroutput on size 1000000
> > SQL>
> > SQL> exec nobind_example('ALLEN')
> > select count(*) from emp where ename = 'ALLEN'
> > 1
>
> > PL/SQL procedure successfully completed.
>
> > SQL> exec bind_example('ALLEN')
> > select count(*) from emp where ename = :1
> > 1
>
> > PL/SQL procedure successfully completed.
>
> > SQL>
>
> > Thus the second example generates a query which can be reused with
> > differing passed parameter values; the first does not.
>
> > David Fitzjarrell
>
> David,
>
> Maybe I'm just not seeing it.  But if you use a bind varialbe (:1) or
> you use concatenation (|| v_variable), don't both queries get
> dynamically generated as both are replacing the variable with a value?- Hide quoted text -
>
> - Show quoted text -

You're not seeing it, as the results of both operations were displayed in my last post:

v_sqlstr:='select count(*) from emp where ename = '''|| p_var||'''';

produces

select count(*) from emp where ename = 'ALLEN'

Each pass through with a different p_var value creates a different query string to parse, whereas:

v_sqlstr:='select count(*) from emp where ename = :1';

produces

select count(*) from emp where ename = :1

EVERY time this code is executed, regardless of the value of p_var

If I execute the first no-bind-variable example 100 times, with 100 different values for p_var, 100 different query strings are generated, each one requiring a hard parse and occupying space in the SQL area and none are likely to be reused; if I execute the bind-variable example 100 times, with the same 100 values for p_var, only ONE query string is generated, and it is reused 99 times. And it's not that the values get replaced, it's HOW and WHEN that replacement occurs. In the first example the replacement occurs before the parse, and it generates a unique SQL statement for each unique value supplied to p_var, and in the second the value is replaced after parse time (hard or soft) which allows for reusable code (the driving force behind using bind variables). There is a big difference between the two operations. Please read here:

http://download.oracle.com/docs/cd/B19306_01/server.102/b14220/sqlplsql.htm#sthref3468

to hopefully clear up any misunderstandings you have.

David Fitzjarrell Received on Tue Dec 30 2008 - 09:45:57 CST