[20160307]绑定变量的分配长度3.txt
--如果绑定变量中字符串分配占用空间的长度变化，oracle会建立子光标。
--参考连接：
http://blog.itpub.net/267265/viewspace-1993495/
http://blog.itpub.net/267265/viewspace-2024389/
--oracle 可以通过一个10503事件设置大的缓存：
$ oerr ora 10503
10503, 00000, "enable user-specified graduated bind lengths"
// *Cause:
// *Action:
--oracle 这样设置，一定有一定的道理，估计跟内存的使用有关。
1.环境：
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;
--确定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, '父游标句柄地址',
'子游标句柄地址')
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$kglob
WHERE kglobt03 = '&1' or kglhdpar='&1' or kglhdadr='&1' or KGLNAHSH= &1;
SYS@book> @ &r/sharepool/shp4 9mrd273576n14
old 17: WHERE kglobt03 = '&1' or kglhdpar='&1' or kglhdadr='&1'
new 17: WHERE kglobt03 = '9mrd273576n14' or kglhdpar='9mrd273576n14' or kglhdadr='9mrd273576n14'
TEXT KGLHDADR KGLHDPAR C40 KGLOBHD0 KGLOBHD6 KGLOBHS0 KGLOBHS6 KGLOBT16 N0_6_16 N20 KGLNAHSH KGLOBT03 KGLOBT09
-------------- ---------------- ---------------- ---------------------------------------- ---------------- ---------------- ---------- ---------- ---------- --------- ---------- ---------- ------------- ----------
子游标句柄地址 00000000858419B8 0000000085935A28 select count(*) from t where c1=:instrin 000000007CAD9978 000000007D0D0770 4528 8088 5570 18186 18186 3396554788 9mrd273576n14 0
子游标句柄地址 000000007CA388A0 0000000085935A28 select count(*) from t where c1=:instrin 000000007C9ACF48 000000007D0D0BD8 4528 8088 5570 18186 18186 3396554788 9mrd273576n14 1
子游标句柄地址 000000007CAF20C0 0000000085935A28 select count(*) from t where c1=:instrin 000000007CBE3660 000000007D39A188 8600 12144 5570 26314 26314 3396554788 9mrd273576n14 2
子游标句柄地址 000000007CACE500 0000000085935A28 select count(*) from t where c1=:instrin 000000007CB1F3E0 000000007D39A4D0 8600 12144 5570 26314 26314 3396554788 9mrd273576n14 3
父游标句柄地址 0000000085935A28 0000000085935A28 select count(*) from t where c1=:instrin 000000007CB497E0 00 8816 0 0 8816 8816 3396554788 9mrd273576n14 65535
--KGLOBT09表示child_number,观察2，3的子光标，可以发现堆0，堆6 消耗的空间很大。oracle这样分级应该从节约共享内存的需要考虑。
--从v$sql视图也可以发现问题。
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就是父游标。我以前的判断是kglhdadr=KGLHDPAR相等就是父游标。