概述
我们知道Oracle在以下的版本中，为了防止产生过多的子游标，增加了子游标个数限定的功能。
UNIX/Linux 平台:
o PSU 11.2.0.2.2 以后
o PSU 11.1.0.7.7 以后
Windows 平台 :
o 11.2.0.2 Patch 3 以后
o 11.1.0.7 Patch 38 以后
即：当子游标个数超过限定数时，该功能会把父游标无效化，重新生成一个父游标。
子游标个数限定的功能，在各个版本上的设置方法如下：
- 11.1.0.7
_cursor_features_enabled=18
event = "106001 trace name context forever, level XXX "
- 11.2.0.1
_cursor_features_enabled=34
event = "106001 trace name context forever, level XXX "
- 11.2.0.2
_cursor_features_enabled=1026
event = "106001 trace name context forever, level XXX "
- 11.2.0.3以后版本
_cursor_obsolete_threshold=XXX
* 其中XXX 为限定的子游标个数
11.2.0.3以后的版本限定功能默认有效并且默认值如下：
11.2.0.3: 100
11.2.0.4以后: 1024
本测试例基于11.2.0.2.2数据库版本，验证该子游标个数限定的功能。
读者也可以参考测试方法和过程，对其他任意版本进行验证。
测试
测试内容主要包括如下：
1.未开启子游标个数限定的功能时的数据库动作。
2.开启子游标个数限定的功能时的数据库动作
3.optimizer_feature_enable参数是否会影响子游标个数限定的功能
准备测试数据
本次测试通过系统提供的Scott Schema进行数据准备。
---建立测试用户
SQL> create user testc1 identified by testc1;
SQL> grant dba to testc1;
SQL> create user testc2 identified by testc2;
SQL> grant dba to testc2;
SQL> create user testc3 identified by testc3;
SQL> grant dba to testc3;
SQL> create user testc4 identified by testc4;
SQL> grant dba to testc4;
SQL> create user testc5 identified by testc5;
SQL> grant dba to testc5;
---为每个测试用户创建同名的表
SQL> conn testc1/testc1
SQL> create table emp as select * from scott.emp;
SQL> conn testc2/testc2
SQL> create table emp as select * from scott.emp;
SQL> conn testc3/testc3
SQL> create table emp as select * from scott.emp;
SQL> conn testc4/testc4
SQL> create table emp as select * from scott.emp;
SQL> conn testc5/testc5
SQL> create table emp as select * from scott.emp;
未开启子游标个数限定的功能时的数据库动作
不同的用户执行相同的SQL语句时，Oracle会进行语义检查，由于各个用户的权限以及查询对象所在的Schema不同，相同的父游标（SQL文）下会生成多个子游标。
----不同的用户执行相同的SQL语句
SQL> conn scott/tiger
SQL> select /* Cursor TEST */ * from emp where ENAME= 'WARD';
SQL> conn testc1/testc1
SQL> select /* Cursor TEST */ * from emp where ENAME= 'WARD';
SQL> conn testc2/testc2
SQL> select /* Cursor TEST */ * from emp where ENAME= 'WARD';
SQL> conn testc3/testc3
SQL> select /* Cursor TEST */ * from emp where ENAME= 'WARD';
SQL> conn testc4/testc4
SQL> select /* Cursor TEST */ * from emp where ENAME= 'WARD';
SQL> conn testc5/testc5
SQL> select /* Cursor TEST */ * from emp where ENAME= 'WARD';
----通过v$sql_shared_cursor查看子游标的生成情况
SQL> conn /as sysdba
----查看SQL ID
SQL> select SQL_ID,SQL_FULLTEXT from V$SQL where upper(SQL_FULLTEXT) like upper('%Cursor TEST %');
SQL_ID
-------------
SQL_FULLTEXT
-------------------------------------------------------------------------------
9kma2mah0qmbj
select /* Cursor TEST */ * from emp where ENAME= 'WARD'
...
---子游标的生成情况
SQL> set linesize 500
SQL> select * from v$sql_shared_cursor where sql_id='9kma2mah0qmbj';
SQL_ID ADDRESS CHILD_ADDRESS CHILD_NUMBER U S O O S L F E B P I S T A B D L T B I I R L I O E M U T N F A P T D L D B P C S C P T M B M R O P M F L P L A F L R L H P B U REASON
------------- ---------------- ---------------- ------------ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - --------------------------------------------------------------------------------
9kma2mah0qmbj 0000000089399910 000000008915C338 0 N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N <ChildNode><ChildNumber>0</ChildNumber><ID>37</ID><reason>Authorization Check fa
9kma2mah0qmbj 0000000089399910 00000000891E4B68 1 N N N N N N N N N N N N N Y N N N Y N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N <ChildNode><ChildNumber>1</ChildNumber><ID>37</ID><reason>Authorization Check fa
9kma2mah0qmbj 0000000089399910 00000000891FB5F8 2 N N N N N N N N N N N N N Y N N N Y N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N <ChildNode><ChildNumber>2</ChildNumber><ID>37</ID><reason>Authorization Check fa
9kma2mah0qmbj 0000000089399910 000000008B8D22A0 3 N N N N N N N N N N N N N Y N N N Y N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N <ChildNode><ChildNumber>3</ChildNumber><ID>37</ID><reason>Authorization Check fa
9kma2mah0qmbj 0000000089399910 000000008A948C48 4 N N N N N N N N N N N N N Y N N N Y N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N <ChildNode><ChildNumber>4</ChildNumber><ID>37</ID><reason>Authorization Check fa
9kma2mah0qmbj 0000000089399910 000000008921D318 5 N N N N N N N N N N N N N Y N N N Y N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N
6 rows selected.
我们可以看到未开启子游标个数限定的功能时，生成了包括ChildNumber：0~5一共6个子游标。
2.开启子游标个数限定的功能时的数据库动作
下面我们测试一下开启子游标个数限定的功能时的数据库动作，
--查看数据库的设定(optimizer_features_enable=11.2.0.2)
SQL> conn /as sysdba
SQL> show parameter optimizer_features_enable
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
optimizer_features_enable string 11.2.0.2
--开启子游标个数限定的功能,设置子游标上限为3
SQL> alter system set "_cursor_features_enabled"=1026 scope=spfile;
System altered.
SQL> alter system set event = "106001 trace name context forever, level 3 " scope=spfile;
System altered.
SQL> shutdown abort
ORACLE instance shut down.
SQL> startup
ORACLE instance started.
Total System Global Area 839282688 bytes
Fixed Size 2231128 bytes
Variable Size 666895528 bytes
Database Buffers 163577856 bytes
Redo Buffers 6578176 bytes
Database mounted.
Database opened.
---重启数据库查看设定状况
SQL> set pagesize 100
set linesize 200
col Parameter format a40
col Description format a50
col Value format a40SQL> SQL> SQL> SQL>
SQL> select a.ksppinm "Parameter",a.KSPPDESC "Description",b.ksppstvl "Value"
from x$ksppi a, x$ksppcv b where a.indx = b.indx and a.ksppinm like '_cursor_features_enabled';
2
Parameter Description Value
--------------------------- -------------------------------------- ----------
_cursor_features_enabled Shared cursor features enabled bits. 1026 ★
SQL> oradebug setmypid
Statement processed.
SQL> oradebug eventdump system
106001 trace name context forever, level 3 ★
SQL>
----不同的用户执行相同的SQL语句
SQL> conn scott/tiger
SQL> select /* Cursor TEST */ * from emp where ENAME= 'WARD';
SQL> conn testc1/testc1
SQL> select /* Cursor TEST */ * from emp where ENAME= 'WARD';
SQL> conn testc2/testc2
SQL> select /* Cursor TEST */ * from emp where ENAME= 'WARD';
SQL> conn testc3/testc3
SQL> select /* Cursor TEST */ * from emp where ENAME= 'WARD';
SQL> conn testc4/testc4
SQL> select /* Cursor TEST */ * from emp where ENAME= 'WARD';
SQL> conn testc5/testc5
SQL> select /* Cursor TEST */ * from emp where ENAME= 'WARD';
----通过v$sql查看各个游标的情况
SQL> select SQL_ID,SQL_FULLTEXT,IS_OBSOLETE,IS_SHAREABLE from V$SQL
where upper(SQL_FULLTEXT) like upper('%Cursor TEST %'); 2
SQL_ID SQL_FULLTEXT I I
------------- -------------------------------------------------------------------------------- - -
9kma2mah0qmbj select /* Cursor TEST */ * from emp where ENAME= 'WARD' Y Y★IS_OBSOLETE为Y,游标被废弃
9kma2mah0qmbj select /* Cursor TEST */ * from emp where ENAME= 'WARD' Y Y★IS_OBSOLETE为Y,游标被废弃
9kma2mah0qmbj select /* Cursor TEST */ * from emp where ENAME= 'WARD' Y Y★IS_OBSOLETE为Y,游标被废弃
9kma2mah0qmbj select /* Cursor TEST */ * from emp where ENAME= 'WARD' N Y
9kma2mah0qmbj select /* Cursor TEST */ * from emp where ENAME= 'WARD' N Y
9kma2mah0qmbj select /* Cursor TEST */ * from emp where ENAME= 'WARD' N Y
a1t30rf4cay7b select SQL_ID,SQL_FULLTEXT,IS_OBSOLETE,IS_SHAREABLE from V$SQL N Y
where upper(SQL_F
7 rows selected.
----通过v$sql_shared_cursor查看子游标的生成情况
SQL> select * from v$sql_shared_cursor where sql_id='9kma2mah0qmbj';
SQL_ID ADDRESS CHILD_ADDRESS CHILD_NUMBER U S O O S L F E B P I S T A B D L T B I I R L I O E M U T N F A P T D L D B P C S C P T M B M R O P M F L P L A F L R L H P B U
------------- ---------------- ---------------- ------------ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
REASON
--------------------------------------------------------------------------------
9kma2mah0qmbj 000000008AD768F8 000000008AD76498 0 N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N
<ChildNode><ChildNumber>0</ChildNumber><ID>37</ID><reason>Authorization Check fa
9kma2mah0qmbj 000000008AD768F8 000000008AFFEA98 1 N N N N N N N N N N N N N Y N N N Y N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N
<ChildNode><ChildNumber>1</ChildNumber><ID>37</ID><reason>Authorization Check fa
9kma2mah0qmbj 000000008AD768F8 0000000091EBC028 2 N N N N N N N N N N N N N Y N N N Y N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N
<ChildNode><ChildNumber>2</ChildNumber><ID>37</ID><reason>Authorization Check fa
9kma2mah0qmbj 000000008BCA58A8 000000008BCAA430 0 N N N N N N N N N N N N N Y N N N Y N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N
<ChildNode><ChildNumber>0</ChildNumber><ID>37</ID><reason>Authorization Check fa
9kma2mah0qmbj 000000008BCA58A8 000000008BCA5008 1 N N N N N N N N N N N N N Y N N N Y N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N
<ChildNode><ChildNumber>1</ChildNumber><ID>37</ID><reason>Authorization Check fa
9kma2mah0qmbj 000000008BCA58A8 000000008AD5A678 2 N N N N N N N N N N N N N Y N N N Y N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N
6 rows selected.
我们可以看到在开启子游标个数限定的功能后，当子游标个数超过限定数，该功能会把父游标无效，重新生成一个父游标。
3.optimizer_feature_enable参数是否会影响子游标个数限定的功能
我们知道Oracle在以下的版本中，子游标个数限定的功能才能有有效。
UNIX/Linux 平台:
o PSU 11.2.0.2.2 以后
o PSU 11.1.0.7.7 以后
那么在PSU11.2.0.2.2的版本上，optimizer_feature_enable=11.1.0.6时的数据库动作会是怎样的呢？
下面测试一下optimizer_feature_enable参数是否会影响子游标个数限定的功能
--查看并变更数据库的设定(optimizer_features_enable=11.1.0.6)
SQL> show parameter optimizer_features_enable
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
optimizer_features_enable string 11.2.0.2
SQL> alter system set optimizer_features_enable='11.1.0.6';
System altered.
SQL> show parameter optimizer_features_enable
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
optimizer_features_enable string 11.1.0.6
SQL>
SQL> shutdown abort
ORACLE instance shut down.
SQL> startup
ORACLE instance started.
Total System Global Area 839282688 bytes
Fixed Size 2231128 bytes
Variable Size 666895528 bytes
Database Buffers 163577856 bytes
Redo Buffers 6578176 bytes
Database mounted.
Database opened.
--开启子游标个数限定的功能,设置子游标上限为3
SQL> show parameter optimizer_features_enable
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
optimizer_features_enable string 11.1.0.6
SQL> set pagesize 100
set linesize 200
col Parameter format a40
col Description format a50
col Value format a40SQL> SQL> SQL> SQL>
SQL> select a.ksppinm "Parameter",a.KSPPDESC "Description",b.ksppstvl "Value"
from x$ksppi a, x$ksppcv b where a.indx = b.indx and a.ksppinm like '_cursor_features_enabled'; 2
Parameter Description Value
---------------------------------------- -------------------------------------------------- ----------------------------------------
_cursor_features_enabled Shared cursor features enabled bits. 1026
SQL> oradebug setmypid
Statement processed.
SQL> oradebug eventdump system
106001 trace name context forever, level 3
SQL>
----不同的用户执行相同的SQL语句
conn scott/tiger
select /* Cursor TEST */ * from emp where ENAME= 'WARD';
conn testc1/testc1
select /* Cursor TEST */ * from emp where ENAME= 'WARD';
conn testc2/testc2
select /* Cursor TEST */ * from emp where ENAME= 'WARD';
conn testc3/testc3
select /* Cursor TEST */ * from emp where ENAME= 'WARD';
conn testc4/testc4
select /* Cursor TEST */ * from emp where ENAME= 'WARD';
conn testc5/testc5
select /* Cursor TEST */ * from emp where ENAME= 'WARD';
----通过v$sql查看各个游标的情况
SQL> select SQL_ID,SQL_FULLTEXT,IS_OBSOLETE,IS_SHAREABLE from V$SQL
where upper(SQL_FULLTEXT) like upper('%Cursor TEST %'); 2
SQL_ID SQL_FULLTEXT I I
------------- -------------------------------------------------------------------------------- - -
9kma2mah0qmbj select /* Cursor TEST */ * from emp where ENAME= 'WARD' Y Y★IS_OBSOLETE为Y,游标被废弃
9kma2mah0qmbj select /* Cursor TEST */ * from emp where ENAME= 'WARD' Y Y★IS_OBSOLETE为Y,游标被废弃
9kma2mah0qmbj select /* Cursor TEST */ * from emp where ENAME= 'WARD' Y Y★IS_OBSOLETE为Y,游标被废弃
9kma2mah0qmbj select /* Cursor TEST */ * from emp where ENAME= 'WARD' N Y
9kma2mah0qmbj select /* Cursor TEST */ * from emp where ENAME= 'WARD' N Y
9kma2mah0qmbj select /* Cursor TEST */ * from emp where ENAME= 'WARD' N Y
a1t30rf4cay7b select SQL_ID,SQL_FULLTEXT,IS_OBSOLETE,IS_SHAREABLE from V$SQL N Y
where upper(SQL_F
7 rows selected.
----通过v$sql_shared_cursor查看子游标的生成情况
SQL> select * from v$sql_shared_cursor where sql_id='9kma2mah0qmbj';
SQL_ID ADDRESS CHILD_ADDRESS CHILD_NUMBER U S O O S L F E B P I S T A B D L T B I I R L I O E M U T N F A P T D L D B P C S C P T M B M R O P M F L P L A F L R L H P B U
------------- ---------------- ---------------- ------------ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
REASON
--------------------------------------------------------------------------------
9kma2mah0qmbj 000000008ADA3E28 000000008ADA39C8 0 N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N
<ChildNode><ChildNumber>0</ChildNumber><ID>37</ID><reason>Authorization Check fa
9kma2mah0qmbj 000000008ADA3E28 0000000091EBB508 1 N N N N N N N N N N N N N Y N N N Y N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N
<ChildNode><ChildNumber>1</ChildNumber><ID>37</ID><reason>Authorization Check fa
9kma2mah0qmbj 000000008ADA3E28 000000008AFC3118 2 N N N N N N N N N N N N N Y N N N Y N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N
<ChildNode><ChildNumber>2</ChildNumber><ID>37</ID><reason>Authorization Check fa
9kma2mah0qmbj 000000008BC55728 000000008BC555C8 0 N N N N N N N N N N N N N Y N N N Y N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N
<ChildNode><ChildNumber>0</ChildNumber><ID>37</ID><reason>Authorization Check fa
9kma2mah0qmbj 000000008BC55728 000000008BC58FC8 1 N N N N N N N N N N N N N Y N N N Y N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N
<ChildNode><ChildNumber>1</ChildNumber><ID>37</ID><reason>Authorization Check fa
9kma2mah0qmbj 000000008BC55728 000000008BF91F90 2 N N N N N N N N N N N N N Y N N N Y N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N
6 rows selected.
我们可以看到optimizer_features_enable=11.1.0.6时在开启子游标个数限定的功能后，当子游标个数超过限定数，该功能也会把父游标无效，重新生成一个父游标。
所以子游标个数限定的功能只跟数据库的版本有关，optimizer_features_enable的设定变化并不影响子游标个数限定的功能。
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