[20180803]cursor_sharing = force.txt

[20180803]cursor_sharing = force.txt

--//連結:https://jonathanlewis.wordpress.com/2018/06/23/cursor_sharing-force/
--//重複測試:

SCOTT@test01p> @ ver1

PORT_STRING                    VERSION        BANNER                                                                               CON_ID
------------------------------ -------------- -------------------------------------------------------------------------------- ----------
IBMPC/WIN_NT64-9.1.0           12.1.0.1.0     Oracle Database 12c Enterprise Edition Release 12.1.0.1.0 - 64bit Production              0

create table t1
as
select
        rownum            n1,
        rownum            n2,
        lpad(rownum,10)   small_vc,
        rpad('x',100,'x') padding
from dual
connect by
        level <= 1e4
;

alter system flush shared_pool;
alter session set cursor_sharing=force;

declare
        m_ct number;
        m_n1 number := 20;
begin
        execute immediate
                'select /*+ trace this */ count(*) from t1 where n2 = 15 and n1 = :b1'
                into m_ct using m_n1;
        dbms_output.put_line(m_ct);

        execute immediate
                'select /*+ trace this too */ count(*) from t1 where n1 = 15 and n2 = 15'
                into m_ct;
        dbms_output.put_line(m_ct);
end;
/

--//alter session set cursor_sharing=exact;


select sql_id, parse_calls, executions, rows_processed, sql_text
from   v$sql
where  sql_text like 'select%trace this%' and    sql_text not like '%v$sql%' ;

SQL_ID        PARSE_CALLS EXECUTIONS ROWS_PROCESSED SQL_TEXT
------------- ----------- ---------- -------------- ----------------------------------------------------------------------------------------------------
cbu4s78h5pfj5           1          1              1 select /*+ trace this too */ count(*) from t1 where n1 = :"SYS_B_0" and n2 = :"SYS_B_1"
cru67sufptx8x           1          1              1 select /*+ trace this */ count(*) from t1 where n2 = 15 and n1 = :b1

--//你可以發現有變數和常量的語句沒有發生轉換,很奇怪.而2個是變數的語句發生了轉換.
--//如果在sqlplus下執行:

alter session set cursor_sharing=force;
variable b1 number
exec :b1 := 15;
select /*+ SQL*Plus session */ count(*) from t1 where n2 = 15 and n1 = :b1;

select sql_id, parse_calls, executions, rows_processed, sql_text
from v$sql
where sql_text like 'select%Plus session%' and        sql_text not like '%v$sql%' ;

SQL_ID        PARSE_CALLS EXECUTIONS ROWS_PROCESSED SQL_TEXT
------------- ----------- ---------- -------------- ----------------------------------------------------------------------------------------------
gq2qy2a9yuta7           1          1              1 select /*+ SQL*Plus session */ count(*) from t1 where n2 = :"SYS_B_0" and n1 = :b1

--//而在sqlplus執行發生了轉換.