[20180819]關於父子遊標問題(11g).txt

--//sql語句存在父子遊標,子遊標堆6在父遊標堆0裏面.
--//如果存在許多子遊標的情況下,父遊標堆0是否大小是發生變化呢.測試看看.
--//另外11g引入參數_cursor_obsolete_threshold限制子光標的數量,測試它的一些控制機制.

1.環境:
--//session 1:
SCOTT@book> @ 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

SCOTT@book> SELECT count(*) FROM dept WHERE deptno=10;
COUNT(*)
----------
1
--//確定sql_id=2xw4k6w7wc5ka.

--//session 2:
SYS@book> @ &r/hide _cursor_obsolete_threshold
NAME DESCRIPTION DEFAULT_VALUE SESSION_VALUE SYSTEM_VALUE
-------------------------- ---------------------------------------------- ------------- ------------- ------------
_cursor_obsolete_threshold Number of cursors per parent before obsoletion TRUE 1024 1024

--//退出session 1,刷新共享池,清除該語句在共享池.這樣才能清除幹凈.
SYS@book> alter system flush shared_pool;
System altered.

2.建立測試腳本:
$ cat aa.sql
DECLARE
l_count PLS_INTEGER;
BEGIN
FOR i IN 1..&&2
LOOP
EXECUTE IMMEDIATE ‘ALTER SESSION SET optimizer_index_caching = ‘||i;
FOR j IN 1..&&1
LOOP
EXECUTE IMMEDIATE ‘ALTER SESSION SET optimizer_index_cost_adj = ‘||j;
EXECUTE IMMEDIATE ‘SELECT count(*) FROM dept WHERE deptno=10‘ into l_count;
END LOOP;
END LOOP;
END;
/
--//執行如上腳本,能產生許多子光標.主要是因為環境變量發生了變化.

--//session 1:
SCOTT@book> @ aa.sql 1 64
PL/SQL procedure successfully completed.

3.查看父子遊標情況:
--//session 2:
SYS@book> @ &r/sharepool/shp4z 2xw4k6w7wc5ka 0
TEXT KGLHDADR KGLHDPAR C40 KGLHDLMD KGLHDPMD KGLOBHD0 KGLOBHD6 KGLOBHS0 KGLOBHS6 KGLOBT16 N0_6_16 N20 KGLNAHSH KGLOBT03 KGLOBT09
-------------- ---------------- ---------------- ---------------------------------------- ---------- ---------- ---------------- ---------------- ---------- ---------- ---------- --------- ---------- ---------- ------------- ----------
父遊標句柄地址 000000007CBC2C60 000000007CBC2C60 SELECT count(*) FROM dept WHERE deptno=1 1 0 000000007CBC2BA8 00 82104 0 0 82104 82104 264640074 2xw4k6w7wc5ka 65535

--//查看父遊標堆0的chunk:
select a.* from x$ksmsp a where a.ksmchpar=hextoraw(‘000000007CBC2BA8‘)
ADDR INDX INST_ID KSMCHIDX KSMCHDUR KSMCHCOM KSMCHPTR KSMCHSIZ KSMCHCLS KSMCHTYP KSMCHPAR
---------------- ---------- ---------- ---------- ---------- ---------------- ---------------- ---------- -------- ---------- ----------------
00007F8F6AF85568 1634 1 1 1 KGLH0^fc6164a 000000007DB3C420 4096 freeabl 0 000000007CBC2BA8
00007F8F6AF5A1F8 2515 1 1 1 KGLH0^fc6164a 000000007D879970 4096 freeabl 0 000000007CBC2BA8
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
00007F8F6AF5EA40 2676 1 1 1 KGLH0^fc6164a 000000007D7C2F20 4096 freeabl 0 000000007CBC2BA8
00007F8F6AF55250 3713 1 1 1 KGLH0^fc6164a 000000007D342488 4096 freeabl 0 000000007CBC2BA8
00007F8F6AF450F0 4407 1 1 1 KGLH0^fc6164a 000000007CE8C5F8 4096 freeabl 0 000000007CBC2BA8
00007F8F6AF47AC0 4471 1 1 1 KGLH0^fc6164a 000000007CE6D850 4096 freeabl 0 000000007CBC2BA8
00007F8F6AF30440 4856 1 1 1 KGLH0^fc6164a 000000007CC973C8 4096 freeabl 0 000000007CBC2BA8
00007F8F6AF33E80 4965 1 1 1 KGLH0^fc6164a 000000007CBD41F0 4096 freeabl 0 000000007CBC2BA8
00007F8F6B0A1400 5593 1 1 1 KGLH0^fc6164a 000000007C7F4F60 4096 freeabl 0 000000007CBC2BA8
00007F8F6B08CD28 6025 1 1 1 KGLH0^fc6164a 000000007C55FC10 4096 freeabl 0 000000007CBC2BA8
00007F8F6B0907B0 6226 1 1 1 KGLH0^fc6164a 000000007C442F48 4096 freeabl 0 000000007CBC2BA8
00007F8F6B07A300 6652 1 1 1 KGLH0^fc6164a 000000007C137798 4096 freeabl 0 000000007CBC2BA8
00007F8F6B070CD8 7591 1 1 1 KGLH0^fc6164a 000000007BC7D898 4096 freeabl 0 000000007CBC2BA8
00007F8F6B072158 7717 1 1 1 KGLH0^fc6164a 000000007BB93BC0 4096 freeabl 0 000000007CBC2BA8
00007F8F6B074238 7807 1 1 1 KGLH0^fc6164a 000000007BB49798 4096 freeabl 0 000000007CBC2BA8
00007F8F6B0754B8 7846 1 1 1 KGLH0^fc6164a 000000007BB19348 4096 freeabl 0 000000007CBC2BA8
00007F8F6B058C38 8653 1 1 1 KGLH0^fc6164a 000000007B62C700 4096 freeabl 0 000000007CBC2BA8
00007F8F6B05AFB8 8778 1 1 1 KGLH0^fc6164a 000000007B5A06E8 4096 freeabl 0 000000007CBC2BA8
00007F8F6B05C6B0 8804 1 1 1 KGLH0^fc6164a 000000007B588C38 4096 freeabl 0 000000007CBC2BA8
00007F8F6B05DDA8 8830 1 1 1 KGLH0^fc6164a 000000007B55FD78 4096 recr 4095 000000007CBC2BA8
00007F8F6B02A960 8930 1 1 1 KGLH0^fc6164a 000000007B4D8640 4096 freeabl 0 000000007CBC2BA8
00007F8F6B02A490 8944 1 1 1 KGLH0^fc6164a 000000007B4AAFF0 4096 freeabl 0 000000007CBC2BA8
22 rows selected.
--//可以發現如果產生子光標很多,父遊標堆0的chunk也會很多,不像1個子光標的情況下僅僅1個chunk.

--//查看父遊標堆0的描述符chunk:
SELECT * FROM x$ksmsp WHERE TO_NUMBER (‘000000007CBC2BA8‘, ‘xxxxxxxxxxxxxxxx‘) between TO_NUMBER(KSMCHPTR, ‘xxxxxxxxxxxxxxxx‘) and TO_NUMBER(KSMCHPTR, ‘xxxxxxxxxxxxxxxx‘)+KSMCHSIZ
ADDR INDX INST_ID KSMCHIDX KSMCHDUR KSMCHCOM KSMCHPTR KSMCHSIZ KSMCHCLS KSMCHTYP KSMCHPAR
---------------- ---------- ---------- ---------- ---------- ---------------- ---------------- ---------- -------- ---------- ----------------
00007F8F6AF337F8 4997 1 1 1 KGLDA 000000007CBC2B40 240 freeabl 0 00

SYS@book> @ &r/sharepool/shp4 2xw4k6w7wc5ka 0
TEXT KGLHDADR KGLHDPAR C40 KGLHDLMD KGLHDPMD KGLHDIVC KGLOBHD0 KGLOBHD6 KGLOBHS0 KGLOBHS6 KGLOBT16 N0_6_16 N20 KGLNAHSH KGLOBT03 KGLOBT09
-------------- ---------------- ---------------- ---------------------------------------- ---------- ---------- ---------- ---------------- ---------------- ---------- ---------- ---------- --------- ---------- ---------- ------------- ----------
子遊標句柄地址 000000007CBC27E0 000000007CBC2C60 SELECT count(*) FROM dept WHERE deptno=1 0 0 0 000000007CBC2728 000000007B5604E8 4488 8088 80634 93210 93210 264640074 2xw4k6w7wc5ka 0
子遊標句柄地址 000000007C6C4A90 000000007CBC2C60 SELECT count(*) FROM dept WHERE deptno=1 0 0 0 000000007C6C49D8 000000007B560AB0 4488 8088 80634 93210 93210 264640074 2xw4k6w7wc5ka 1
子遊標句柄地址 000000007DA59628 000000007CBC2C60 SELECT count(*) FROM dept WHERE deptno=1 0 0 0 000000007DA59570 000000007B4D89C0 4488 8088 80634 93210 93210 264640074 2xw4k6w7wc5ka 2
子遊標句柄地址 000000007D66E770 000000007CBC2C60 SELECT count(*) FROM dept WHERE deptno=1 0 0 0 000000007D66E6B8 000000007B4D8E80 4488 8088 80634 93210 93210 264640074 2xw4k6w7wc5ka 3
...//太長
子遊標句柄地址 000000007B693320 000000007CBC2C60 SELECT count(*) FROM dept WHERE deptno=1 1 0 0 000000007B693268 000000007D87A1B0 4488 8088 80634 93210 93210 264640074 2xw4k6w7wc5ka 63
父遊標句柄地址 000000007CBC2C60 000000007CBC2C60 SELECT count(*) FROM dept WHERE deptno=1 1 0 0 000000007CBC2BA8 00 82104 0 0 82104 82104 264640074 2xw4k6w7wc5ka 65535
65 rows selected.

--//隨便看看一個子光標堆6的描述符chunk:(KGLOBHD6=000000007D87A1B0)
SELECT * FROM x$ksmsp WHERE TO_NUMBER (‘000000007D87A1B0‘, ‘xxxxxxxxxxxxxxxx‘) between TO_NUMBER(KSMCHPTR, ‘xxxxxxxxxxxxxxxx‘) and TO_NUMBER(KSMCHPTR, ‘xxxxxxxxxxxxxxxx‘)+KSMCHSIZ
ADDR INDX INST_ID KSMCHIDX KSMCHDUR KSMCHCOM KSMCHPTR KSMCHSIZ KSMCHCLS KSMCHTYP KSMCHPAR
---------------- ---------- ---------- ---------- ---------- ---------------- ---------------- ---------- -------- ---------- ----------------
00007F8F6AF6DD40 2621 1 1 1 KGLH0^fc6164a 000000007D879970 4096 freeabl 0 000000007CBC2BA8

--//可以發現堆6的描述符chunk與前面的父遊標堆0的chunk相同,註意看前面下劃線內容.也就是子遊標堆6的描述符chunk在父遊標堆0的chunk中.

4.繼續測試_cursor_obsolete_threshold限制子光標的數量.
--//退出session 1,刷新共享池.
--//session 2:
SYS@book> alter system flush shared_pool;
System altered.

SCOTT@book> alter session set "_cursor_obsolete_threshold"=64;
Session altered.
--//缺省參數1024,有點大,減少到64,這樣好測試一些.

--//session 1:
SCOTT@book> @ aa.sql 1 65
PL/SQL procedure successfully completed.

--//session 2
SYS@book> @ &r/sharepool/shp4z 2xw4k6w7wc5ka 0
TEXT KGLHDADR KGLHDPAR C40 KGLHDLMD KGLHDPMD KGLOBHD0 KGLOBHD6 KGLOBHS0 KGLOBHS6 KGLOBT16 N0_6_16 N20 KGLNAHSH KGLOBT03 KGLOBT09
-------------- ---------------- ---------------- ---------------------------------------- ---------- ---------- ---------------- ---------------- ---------- ---------- ---------- --------- ---------- ---------- ------------- ----------
父遊標句柄地址 000000007BBF0758 000000007BBF0758 SELECT count(*) FROM dept WHERE deptno=1 1 0 000000007DA01CE8 00 82104 0 0 82104 82104 264640074 2xw4k6w7wc5ka 65535
父遊標句柄地址 000000007D0716A0 000000007D0716A0 SELECT count(*) FROM dept WHERE deptno=1 1 0 000000007B442B50 00 4736 0 0 4736 4736 264640074 2xw4k6w7wc5ka 65535
--//產生2個父遊標,註意2條記錄的KGLHDLMD=1.表示還沒有釋放遊標.
--//註:我開始以為會出現多父多子的情況.實際上並不是,查看v$sql視圖就很容易明白.

SYS@book> select address,child_number,IS_OBSOLETE from v$sql where sql_id=‘2xw4k6w7wc5ka‘ and IS_OBSOLETE=‘N‘;
ADDRESS CHILD_NUMBER I
---------------- ------------ -
000000007D0716A0 0 N

SYS@book> select address,IS_OBSOLETE,count(*) from v$sql where sql_id=‘2xw4k6w7wc5ka‘ group by address ,IS_OBSOLETE;
ADDRESS I COUNT(*)
---------------- - ----------
000000007D0716A0 N 1
000000007BBF0758 Y 64
--//可以發現僅僅1個子光標是IS_OBSOLETE=‘N‘.其它IS_OBSOLETE=‘Y‘,共有64個子光標,而且地址也不同(這個地址對應父遊標的地址).繼續測試:
--//父遊標地址000000007BBF0758下的子光標都是IS_OBSOLETE=‘Y‘.
--//session 1:
SCOTT@book> @ aa.sql 1 65
PL/SQL procedure successfully completed.

--//session 2:
SYS@book> @ &r/sharepool/shp4z 2xw4k6w7wc5ka 0
TEXT KGLHDADR KGLHDPAR C40 KGLHDLMD KGLHDPMD KGLOBHD0 KGLOBHD6 KGLOBHS0 KGLOBHS6 KGLOBT16 N0_6_16 N20 KGLNAHSH KGLOBT03 KGLOBT09
-------------- ---------------- ---------------- ---------------------------------------- ---------- ---------- ---------------- ---------------- ---------- ---------- ---------- --------- ---------- ---------- ------------- ----------
父遊標句柄地址 000000007BBF0758 000000007BBF0758 SELECT count(*) FROM dept WHERE deptno=1 0 0 000000007DA01CE8 00 82104 0 0 82104 82104 264640074 2xw4k6w7wc5ka 65535
父遊標句柄地址 000000007D0716A0 000000007D0716A0 SELECT count(*) FROM dept WHERE deptno=1 1 0 000000007B442B50 00 82104 0 0 82104 82104 264640074 2xw4k6w7wc5ka 65535
父遊標句柄地址 000000007B59E0F8 000000007B59E0F8 SELECT count(*) FROM dept WHERE deptno=1 1 0 000000007B59E040 00 4736 0 0 4736 4736 264640074 2xw4k6w7wc5ka 65535

SYS@book> select address,IS_OBSOLETE,count(*) from v$sql where sql_id=‘2xw4k6w7wc5ka‘ group by address ,IS_OBSOLETE;
ADDRESS I COUNT(*)
---------------- - ----------
000000007D0716A0 Y 64
000000007B59E0F8 N 2
000000007BBF0758 Y 64

--//產生2個父遊標,註意後2條記錄的KGLHDLMD=1. 而地址000000007B59E0F8對應的IS_OBSOLETE=‘N‘,其它都是IS_OBSOLETE=‘Y‘.
--//表示父遊標句柄地址=000000007B59E0F8,當前有效(IS_OBSOLETE=‘N‘).繼續測試:

--//session 1:
SCOTT@book> @ aa.sql 1 65
PL/SQL procedure successfully completed.

--//session 2:
SYS@book> @ &r/sharepool/shp4z 2xw4k6w7wc5ka 0
TEXT KGLHDADR KGLHDPAR C40 KGLHDLMD KGLHDPMD KGLOBHD0 KGLOBHD6 KGLOBHS0 KGLOBHS6 KGLOBT16 N0_6_16 N20 KGLNAHSH KGLOBT03 KGLOBT09
-------------- ---------------- ---------------- ---------------------------------------- ---------- ---------- ---------------- ---------------- ---------- ---------- ---------- --------- ---------- ---------- ------------- ----------
父遊標句柄地址 000000007BBF0758 000000007BBF0758 SELECT count(*) FROM dept WHERE deptno=1 0 0 000000007DA01CE8 00 82104 0 0 82104 82104 264640074 2xw4k6w7wc5ka 65535
父遊標句柄地址 000000007D0716A0 000000007D0716A0 SELECT count(*) FROM dept WHERE deptno=1 0 0 000000007B442B50 00 82104 0 0 82104 82104 264640074 2xw4k6w7wc5ka 65535
父遊標句柄地址 000000007B59E0F8 000000007B59E0F8 SELECT count(*) FROM dept WHERE deptno=1 1 0 000000007B59E040 00 82104 0 0 82104 82104 264640074 2xw4k6w7wc5ka 65535
父遊標句柄地址 000000007CB65CB0 000000007CB65CB0 SELECT count(*) FROM dept WHERE deptno=1 1 0 000000007CB65BF8 00 8808 0 0 8808 8808 264640074 2xw4k6w7wc5ka 65535

SYS@book> select address,IS_OBSOLETE,count(*) from v$sql where sql_id=‘2xw4k6w7wc5ka‘ group by address ,IS_OBSOLETE;
ADDRESS I COUNT(*)
---------------- - ----------
000000007D0716A0 Y 64
000000007BBF0758 Y 64
000000007B59E0F8 Y 64
000000007CB65CB0 N 3

--//大家自己看,不再說明.
--//可以發現1個規律.如果當前父遊標下存在64個子光標的情況下,再有子光標產生,該父遊標下的子遊標無效(IS_OBSOLETE=‘Y‘),建立新的父遊標.
--//我前面調用的腳本@ aa.sql 1 65,每次都有1個子光標無法容納,產生1個新的父遊標,這樣3次,這樣新建立的父遊標下就存在3個子光標.

--//如果執行如下,就不會建立新的父遊標.
--//session 1:
SCOTT@book> @ aa.sql 1 61
PL/SQL procedure successfully completed.

--//session 2:
SYS@book> @ &r/sharepool/shp4z 2xw4k6w7wc5ka 0
old 21: WHERE kglobt03 = ‘&1‘ or kglhdpar=‘&1‘ or kglhdadr=‘&1‘ or KGLNAHSH= &2
new 21: WHERE kglobt03 = ‘2xw4k6w7wc5ka‘ or kglhdpar=‘2xw4k6w7wc5ka‘ or kglhdadr=‘2xw4k6w7wc5ka‘ or KGLNAHSH= 0
TEXT KGLHDADR KGLHDPAR C40 KGLHDLMD KGLHDPMD KGLOBHD0 KGLOBHD6 KGLOBHS0 KGLOBHS6 KGLOBT16 N0_6_16 N20 KGLNAHSH KGLOBT03 KGLOBT09
-------------- ---------------- ---------------- ---------------------------------------- ---------- ---------- ---------------- ---------------- ---------- ---------- ---------- --------- ---------- ---------- ------------- ----------
父遊標句柄地址 000000007BBF0758 000000007BBF0758 SELECT count(*) FROM dept WHERE deptno=1 0 0 000000007DA01CE8 00 82104 0 0 82104 82104 264640074 2xw4k6w7wc5ka 65535
父遊標句柄地址 000000007D0716A0 000000007D0716A0 SELECT count(*) FROM dept WHERE deptno=1 0 0 000000007B442B50 00 82104 0 0 82104 82104 264640074 2xw4k6w7wc5ka 65535
父遊標句柄地址 000000007B59E0F8 000000007B59E0F8 SELECT count(*) FROM dept WHERE deptno=1 0 0 000000007B59E040 00 82104 0 0 82104 82104 264640074 2xw4k6w7wc5ka 65535
父遊標句柄地址 000000007CB65CB0 000000007CB65CB0 SELECT count(*) FROM dept WHERE deptno=1 1 0 000000007CB65BF8 00 82104 0 0 82104 82104 264640074 2xw4k6w7wc5ka 65535

SYS@book> select address,IS_OBSOLETE,count(*) from v$sql where sql_id=‘2xw4k6w7wc5ka‘ group by address ,IS_OBSOLETE;
ADDRESS I COUNT(*)
---------------- - ----------
000000007D0716A0 Y 64
000000007BBF0758 Y 64
000000007B59E0F8 Y 64
000000007CB65CB0 N 64
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--//註意看KGLHDLMD=1那行,父遊標句柄地址=000000007CB65CB0.與下劃線看到的地址一致(IS_OBSOLETE=‘N‘).如果我繼續執行
--//session 1:
SCOTT@book> @ aa.sql 1 64
PL/SQL procedure successfully completed.

--//session 2:
SYS@book> @ &r/sharepool/shp4z 2xw4k6w7wc5ka 0
TEXT KGLHDADR KGLHDPAR C40 KGLHDLMD KGLHDPMD KGLOBHD0 KGLOBHD6 KGLOBHS0 KGLOBHS6 KGLOBT16 N0_6_16 N20 KGLNAHSH KGLOBT03 KGLOBT09
-------------- ---------------- ---------------- ---------------------------------------- ---------- ---------- ---------------- ---------------- ---------- ---------- ---------- --------- ---------- ---------- ------------- ----------
父遊標句柄地址 000000007BBF0758 000000007BBF0758 SELECT count(*) FROM dept WHERE deptno=1 0 0 000000007DA01CE8 00 82104 0 0 82104 82104 264640074 2xw4k6w7wc5ka 65535
父遊標句柄地址 000000007D0716A0 000000007D0716A0 SELECT count(*) FROM dept WHERE deptno=1 0 0 000000007B442B50 00 82104 0 0 82104 82104 264640074 2xw4k6w7wc5ka 65535
父遊標句柄地址 000000007B59E0F8 000000007B59E0F8 SELECT count(*) FROM dept WHERE deptno=1 0 0 000000007B59E040 00 82104 0 0 82104 82104 264640074 2xw4k6w7wc5ka 65535
父遊標句柄地址 000000007CB65CB0 000000007CB65CB0 SELECT count(*) FROM dept WHERE deptno=1 1 0 000000007CB65BF8 00 82104 0 0 82104 82104 264640074 2xw4k6w7wc5ka 65535
父遊標句柄地址 000000007CE9EFB8 000000007CE9EFB8 SELECT count(*) FROM dept WHERE deptno=1 1 0 000000007CE9EF00 00 8808 0 0 8808 8808 264640074 2xw4k6w7wc5ka 65535

SYS@book> select address,IS_OBSOLETE,count(*) from v$sql where sql_id=‘2xw4k6w7wc5ka‘ group by address ,IS_OBSOLETE;
ADDRESS I COUNT(*)
---------------- - ----------
000000007CE9EFB8 N 3
000000007CB65CB0 Y 64
000000007D0716A0 Y 64
000000007BBF0758 Y 64
000000007B59E0F8 Y 64

--//奇怪竟然又生產新的父遊標,下面有3個子光標.why?
--//中午自己認真看一遍,突然明白為什麽存在3個子光標,IS_OBSOLETE=‘N‘.

5.一步一步來解析:
--//執行@ aa.sql 1 65, 一個父遊標僅僅有64個子遊標,這樣最後1個語句,生成新父遊標,對應的optimizer_index_caching=65.
--//執行@ aa.sql 1 65, 執行到optimizer_index_caching=64時,該父遊標無法再加入子遊標,生成新父遊標,對應的optimizer_index_caching=64,65.存在2個子光標.
--//執行@ aa.sql 1 65, 執行到optimizer_index_caching=63時,該父遊標無法再加入子遊標,生成新父遊標,對應的optimizer_index_caching=63,64,65.
--//執行@ aa.sql 1 61, 對於父遊標正好有64個子遊標.不會生成新的父遊標.而對應子遊標的optimizer_index_caching=63,64,65,1,2,....,61
--//執行@ aa.sql 1 64, optimizer_index_caching從1,2,..,61都能找到對應的子光標.而當執行optimizer_index_caching=62時,全部子遊標不合適.
--//而且該父遊標下已經存在64個子遊標,這樣該父遊標下全部子遊標變成IS_OBSOLETE=‘Y‘.生成新的父遊標.對應的optimizer_index_caching=62,63,64.存在3個子光標.

--//可以通過一個簡單的測試證明自己的判斷:
--//退出sessioin 1,刷新共享池.
--//session 2:
SYS@book> alter system flush shared_pool;
System altered.

--//session 1,順序執行如下:
SCOTT@book> alter session set "_cursor_obsolete_threshold"=64;
Session altered.

@ aa.sql 1 65
@ aa.sql 1 65
@ aa.sql 1 65
@ aa.sql 1 61

--//建立測試腳本ab.sql:
$ cat ab.sql
DECLARE
l_count PLS_INTEGER;
BEGIN
FOR i IN 62..64
LOOP
EXECUTE IMMEDIATE ‘ALTER SESSION SET optimizer_index_caching = ‘||i;
FOR j IN 1..&&1
LOOP
EXECUTE IMMEDIATE ‘ALTER SESSION SET optimizer_index_cost_adj = ‘||j;
EXECUTE IMMEDIATE ‘SELECT count(*) FROM dept WHERE deptno=10‘ into l_count;
END LOOP;
END LOOP;
END;
/
--//註:僅僅調用執行optimizer_index_caching=62,63,64的情況.

--//session 1
SCOTT@book> @ ab.sql 1
PL/SQL procedure successfully completed.

--//session 2:
SYS@book> @ &r/sharepool/shp4z 2xw4k6w7wc5ka 0
TEXT KGLHDADR KGLHDPAR C40 KGLHDLMD KGLHDPMD KGLOBHD0 KGLOBHD6 KGLOBHS0 KGLOBHS6 KGLOBT16 N0_6_16 N20 KGLNAHSH KGLOBT03 KGLOBT09
-------------- ---------------- ---------------- ---------------------------------------- ---------- ---------- ---------------- ---------------- ---------- ---------- ---------- --------- ---------- ---------- ------------- ----------
父遊標句柄地址 000000007D3E0D18 000000007D3E0D18 SELECT count(*) FROM dept WHERE deptno=1 0 0 000000007D3E0C60 00 82104 0 0 82104 82104 264640074 2xw4k6w7wc5ka 65535
父遊標句柄地址 000000007CD26CF0 000000007CD26CF0 SELECT count(*) FROM dept WHERE deptno=1 0 0 000000007CD26C38 00 82104 0 0 82104 82104 264640074 2xw4k6w7wc5ka 65535
父遊標句柄地址 000000007B4808C0 000000007B4808C0 SELECT count(*) FROM dept WHERE deptno=1 0 0 000000007B480808 00 82104 0 0 82104 82104 264640074 2xw4k6w7wc5ka 65535
父遊標句柄地址 000000007D14F128 000000007D14F128 SELECT count(*) FROM dept WHERE deptno=1 1 0 000000007D14F070 00 82104 0 0 82104 82104 264640074 2xw4k6w7wc5ka 65535
父遊標句柄地址 000000007B9760C8 000000007B9760C8 SELECT count(*) FROM dept WHERE deptno=1 1 0 000000007B976010 00 8808 0 0 8808 8808 264640074 2xw4k6w7wc5ka 65535

SYS@book> select address,IS_OBSOLETE,count(*) from v$sql where sql_id=‘2xw4k6w7wc5ka‘ group by address ,IS_OBSOLETE;
ADDRESS I COUNT(*)
---------------- - ----------
000000007D3E0D18 Y 64
000000007CD26CF0 Y 64
000000007B9760C8 N 3
000000007D14F128 Y 64
000000007B4808C0 Y 64

--//還有3個子遊標,IS_OBSOLETE=‘N‘.
--//測試有點亂,不過還是能基本說明問題.oracle各個版本_cursor_obsolete_threshold參數一直的不斷調整.
--//看來家裏的windows系統12.1.0.1:
SYS@test> @ 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

SYS@test> @ hide _cursor_obsolete_threshold
NAME DESCRIPTION DEFAULT_VALUE SESSION_VALUE SYSTEM_VALUE
-------------------------- ----------------------------------------------- ------------- ------------- ------------
_cursor_obsolete_threshold Number of cursors per parent before obsoletion. FALSE 64 64

--//據說12.2.0.1版本修改為8192.當然重點定位為什麽子光標太多,定位問題很關鍵.
--//我個人感覺1024還是比較合理.

6.附上測試腳本:
--//shp4.sql
column N0_6_16 format 99999999
SELECT DECODE (kglhdadr,
kglhdpar, ‘父遊標句柄地址‘,
‘子遊標句柄地址‘)
text,
kglhdadr,
kglhdpar,
substr(kglnaobj,1,40) c40,
KGLHDLMD,
KGLHDPMD,
-- kglhdivc,
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= &2;

--//shp4z.sql
column N0_6_16 format 99999999
select * from (
SELECT DECODE (kglhdadr,
kglhdpar, ‘父遊標句柄地址‘,
‘子遊標句柄地址‘)
text,
kglhdadr,
kglhdpar,
substr(kglnaobj,1,40) c40,
KGLHDLMD,
KGLHDPMD,
-- kglhdivc,
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= &2
) where kglhdadr=kglhdpar;

[20180819]關於父子遊標問題(11g).txt