Re: How to force Oracle generate a new execution plan

Hello,

One thing I have played with in TEST environment but never in running system (yet) is the following

SQL> create table t as select rownum n1, rownum*2 n2 from dual connect by level <=100;

SQL> select count(1) from t where n1 = 10;

SQL> select count(1) from t where n1 = 10;

SQL> select * from table(dbms_xplan.display_cursor);

SQL> select

        sql_id, child_number, executions, invalidations, object_status

    from

        gv$sql

    where

        sql_id = '41jpjk91rv6a1';

SQL_ID CHILD_NUMBER EXECUTIONS INVALIDATIONS OBJECT_STATUS

• ------------ ---------- ------------- -------------------

41jpjk91rv6a1 0 2 0 VALID

• Invalidating the cursor using dbms_sqldiag,

declare

  v_sql_text clob;

begin

 select sql_fulltext into v_sql_text from gv$sqlarea where sql_id = '41jpjk91rv6a1' and rownum=1;

 sys.dbms_sqldiag_internal.i_create_patch(v_sql_text, 'xxxxx', 'invalidate_cursor');

  sys.dbms_sqldiag.drop_sql_patch('invalidate_cursor');

end;

/

SQL> select

  2 sql_id, child_number, executions, invalidations, object_status

  3 from

  4 gv$sql

  5 where

  6 sql_id = '41jpjk91rv6a1';

SQL_ID CHILD_NUMBER EXECUTIONS INVALIDATIONS OBJECT_STATUS

• ------------ ---------- ------------- -------------------

41jpjk91rv6a1 0 2 1 INVALID_UNAUTH

SQL> select count(1) from t where n1 = 10;

SQL> select

  2 sql_id, child_number, executions, invalidations, object_status

  3 from

  4 gv$sql

  5 where

  6 sql_id = '41jpjk91rv6a1';

SQL_ID CHILD_NUMBER EXECUTIONS INVALIDATIONS OBJECT_STATUS

• ------------ ---------- ------------- -------------------

41jpjk91rv6a1 0 1 1 VALID

Notice that although a new child cursor n°0 has been hard parsed (execution = 1) Oracle is still keeping, in its external x$table, that this cursor

has already been invalidated (invalidations = 1)

Best regards

Mohamed Houri

2016-11-11 0:46 GMT+01:00 Carlos Sierra <carlos.sierra.usa_at_gmail.com>:

> Eriovaldo,
>
> Consider storing your values on a global temporary table and join it.
>
> If for whatever reason that were not possible, please find the SQL_ID and
> send me a SQLd360 for it. I would help you then to identify WHY your plan
> performs poorly. You do not want to “force” a new plan on every execution.
>
> Carlos
>
>
>
> On Nov 10, 2016, at 2:12 PM, Eriovaldo Andrietta <ecandrietta_at_gmail.com>
> wrote:
>
> Hello,
>
> I have a dynamic query that is mounted by a java application.
> This query uses IN (:b1, :b2, :b3 ... :b1000)
>
> When the application submit the sql statment using until 20 bind
> variables, the return is fast.
> When the application submit the sql statment using more than 20 bind
> variables, the return is slow, very slow. Here It maybe using a certain bad
> execution plan.
> The limit of bind variables is 1000.
>
> 1.) How can I do to force Oracle always generate a new execution plan and
> not reuse the plan that is in cache ?
> 2.) Is there a way to clear a execution plan for a specific sql_id ? (I
> have the sql_id that supose is with the bad execution plan).
>
> Is there any hint to do it ?
>
> I cannot use:
> alter system flush BUFFER_CACHE;
> alter system flush SHARED_POOL;
> because I will clear all execution plans of the instance. I would like to
> solve only 1 sql_id.
>
>
> Regards
> Eriovaldo
>
>
>

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Houri Mohamed

Oracle DBA-Developer-Performance & Tuning

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