[20160307]繫結變數的分配長度3.txt

[20160307]繫結變數的分配長度3.txt

--如果繫結變數中字串分配佔用空間的長度變化，oracle會建立子游標。
--參考連線：
http://blog.itpub.net/267265/viewspace-1993495/
http://blog.itpub.net/267265/viewspace-2024389/

--oracle 可以透過一個10503事件設定大的快取：
$ oerr ora 10503
10503, 00000, "enable user-specified graduated bind lengths"
// *Cause:
// *Action:

--oracle 這樣設定，一定有一定的道理，估計跟記憶體的使用有關。

1.環境：

SCOTT@book> @  &r/ver1

PORT_STRING                    VERSION        BANNER
------------------------------ -------------- --------------------------------------------------------------------------------
x86_64/Linux 2.4.xx            11.2.0.4.0     Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production

create table t (c1 varchar2(4000));

-- ALTER SESSION SET EVENTS '10503 trace name context level <buffer length>, forever';
-- ALTER SESSION SET EVENTS '10503 trace name context level 2000, forever';

declare
v_c1 varchar2(4000);
  begin
   for i in 1..4000 loop
     v_c1 := rpad('X',i);
     execute immediate 'select count(*) from t where c1=:instring' using v_c1 ;
    end loop;
end;
/
commit;

--確定sql_id='9mrd273576n14'

SCOTT@book> @ &r/bind_cap 9mrd273576n14
C200
----------------------------------------------------------------------------------------------------------------------------------
select count(*) from t where c1=:instring

SQL_ID        CHILD_NUMBER WAS NAME                   POSITION MAX_LENGTH LAST_CAPTURED       DATATYPE_STRING VALUE_STRING
------------- ------------ --- -------------------- ---------- ---------- ------------------- --------------- --------------------
9mrd273576n14            0 YES :INSTRING                     1         32 2016-03-07 17:06:10 VARCHAR2(32)    X
                         1 YES :INSTRING                     1        128 2016-03-07 17:06:10 VARCHAR2(128)   X
                         2 YES :INSTRING                     1       2000 2016-03-07 17:06:10 VARCHAR2(2000)  X
                         3 YES :INSTRING                     1       4000 2016-03-07 17:06:10 VARCHAR2(4000)  X

$ cat shp4.sql
column N0_6_16 format 99999999
SELECT DECODE (kglhdadr,
               kglhdpar, '父遊標控制程式碼地址',
               '子游標控制程式碼地址')
          text,
       kglhdadr,
       kglhdpar,
       substr(kglnaobj,1,40) c40,
       kglobhd0,
       kglobhd6,
       kglobhs0,kglobhs6,kglobt16,
       kglobhs0+kglobhs6+kglobt16 N0_6_16,
           kglobhs0+kglobhs1+kglobhs2+kglobhs3+kglobhs4+kglobhs5+kglobhs6+kglobt16 N20,
           kglnahsh,
           kglobt03 ,
           kglobt09
  FROM x$kglob
WHERE kglobt03 = '&1'  or kglhdpar='&1' or kglhdadr='&1' or KGLNAHSH= &1;

SYS@book> @ &r/sharepool/shp4 9mrd273576n14
old  17:  WHERE kglobt03 = '&1'  or kglhdpar='&1' or kglhdadr='&1'
new  17:  WHERE kglobt03 = '9mrd273576n14'  or kglhdpar='9mrd273576n14' or kglhdadr='9mrd273576n14'
TEXT           KGLHDADR         KGLHDPAR         C40                                      KGLOBHD0         KGLOBHD6           KGLOBHS0   KGLOBHS6   KGLOBT16   N0_6_16        N20   KGLNAHSH KGLOBT03        KGLOBT09
-------------- ---------------- ---------------- ---------------------------------------- ---------------- ---------------- ---------- ---------- ---------- --------- ---------- ---------- ------------- ----------
子游標控制程式碼地址 00000000858419B8 0000000085935A28 select count(*) from t where c1=:instrin 000000007CAD9978 000000007D0D0770       4528       8088       5570     18186      18186 3396554788 9mrd273576n14          0
子游標控制程式碼地址 000000007CA388A0 0000000085935A28 select count(*) from t where c1=:instrin 000000007C9ACF48 000000007D0D0BD8       4528       8088       5570     18186      18186 3396554788 9mrd273576n14          1
子游標控制程式碼地址 000000007CAF20C0 0000000085935A28 select count(*) from t where c1=:instrin 000000007CBE3660 000000007D39A188       8600      12144       5570     26314      26314 3396554788 9mrd273576n14          2
子游標控制程式碼地址 000000007CACE500 0000000085935A28 select count(*) from t where c1=:instrin 000000007CB1F3E0 000000007D39A4D0       8600      12144       5570     26314      26314 3396554788 9mrd273576n14          3
父遊標控制程式碼地址 0000000085935A28 0000000085935A28 select count(*) from t where c1=:instrin 000000007CB497E0 00                     8816          0          0      8816       8816 3396554788 9mrd273576n14      65535

--KGLOBT09表示child_number,觀察2，3的子游標，可以發現堆0，堆6 消耗的空間很大。oracle這樣分級應該從節約共享記憶體的需要考慮。
--從v$sql檢視也可以發現問題。

SYS@book> select  sql_id,sql_text,SHARABLE_MEM,child_number from  v$sql where sql_id='9mrd273576n14';
SQL_ID        SQL_TEXT                                   SHARABLE_MEM CHILD_NUMBER
------------- ------------------------------------------ ------------ ------------
9mrd273576n14 select count(*) from t where c1=:instring         18186            0
9mrd273576n14 select count(*) from t where c1=:instring         18186            1
9mrd273576n14 select count(*) from t where c1=:instring         26314            2
9mrd273576n14 select count(*) from t where c1=:instring         26314            3

--另外今天才知道KGLOBT09=65535就是父遊標。我以前的判斷是kglhdadr=KGLHDPAR相等就是父遊標。