在最近的一个客户案例中,因为缺少dual同义词,导致ddl语句无法执行。这里_system_trig_enabled参数和upgrade模式两种来解决该问题,整体上来说_system_trig_enabled不用重启数据库终止业务,更加人性化.
缺少dual同义词后果

SQL> create table t_xifenfei_dual as
  2  select * from dba_objects;
select * from dba_objects
              *
ERROR at line 2:
ORA-00604: error occurred at recursive SQL level 1
ORA-00942: table or view does not exist

SQL> alter session set events '942 trace name errorstack level 3';

Session altered.

SQL> create table t_xifenfei_dual as  select * from dba_objects;
create table t_xifenfei_dual as  select * from dba_objects
                                               *
ERROR at line 1:
ORA-00604: error occurred at recursive SQL level 1
ORA-00942: table or view does not exist

--trace文件
*** 2012-09-29 12:37:05.156
ksedmp: internal or fatal error
ORA-00942: table or view does not exist
Current SQL statement for this session:
select dummy from dual where  ora_dict_obj_type = 'SYNONYM' 
AND ora_dict_obj_owner = 'PUBLIC'

--dual 对象
SQL> select object_type,owner from dba_objects where object_name='DUAL';

OBJECT_TYPE         OWNER
------------------- ------------------------------
TABLE               SYS

尝试重建同义词

SQL> create public synonym dual for dual;
create public synonym dual for dual
*
ERROR at line 1:
ORA-00604: error occurred at recursive SQL level 1
ORA-00942: table or view does not exist

_system_trig_enabled参数

SQL> select a.ksppinm name,b.ksppstvl value,a.ksppdesc description
  2    from x$ksppi a,x$ksppcv b
  3   where a.inst_id = USERENV ('Instance')
  4     and b.inst_id = USERENV ('Instance')
  5     and a.indx = b.indx
  6     and upper(a.ksppinm) LIKE upper('%&param%')
  7  order by name
  8  /
Enter value for param: SYSTEM_TRIG_ENABLED
old   6:    and upper(a.ksppinm) LIKE upper('%&param%')
new   6:    and upper(a.ksppinm) LIKE upper('%SYSTEM_TRIG_ENABLED%')

NAME                             VALUE                    DESCRIPTION
-------------------------------- ------------------------ -----------------------------
_system_trig_enabled             TRUE                     are system triggers enabled

设置_SYSTEM_TRIG_ENABLED重建dual同义词

SQL> ALTER SYSTEM SET "_SYSTEM_TRIG_ENABLED"=FALSE SCOPE=MEMORY;

System altered.

SQL> create public synonym dual for dual;

Synonym created.


SQL> ALTER SYSTEM SET "_SYSTEM_TRIG_ENABLED"=true SCOPE=MEMORY;

System altered.

使用upgrade模式创建

SQL> drop PUBLIC SYNONYM dual;

Synonym dropped.

SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup
ORACLE instance started.

Total System Global Area  318767104 bytes
Fixed Size                  1267236 bytes
Variable Size             109054428 bytes
Database Buffers          201326592 bytes
Redo Buffers                7118848 bytes
Database mounted.
Database opened.
SQL> create public synonym dual for dual;
create public synonym dual for dual
*
ERROR at line 1:
ORA-00604: error occurred at recursive SQL level 1
ORA-00942: table or view does not exist


SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup upgrage;
SP2-0714: invalid combination of STARTUP options
SQL> startup upgrape;
SP2-0714: invalid combination of STARTUP options
SQL> startup upgrade
ORACLE instance started.

Total System Global Area  318767104 bytes
Fixed Size                  1267236 bytes
Variable Size             109054428 bytes
Database Buffers          201326592 bytes
Redo Buffers                7118848 bytes
Database mounted.
Database opened.
SQL> create public synonym dual for dual;

Synonym created.

SQL> startup force
ORACLE instance started.

Total System Global Area  318767104 bytes
Fixed Size                  1267236 bytes
Variable Size             109054428 bytes
Database Buffers          201326592 bytes
Redo Buffers                7118848 bytes
Database mounted.
Database opened.

ckpt进程的trace文件中出现类似：9430ms (rw) file: kct.c line: 7800 count: 13 total: 26874ms time: 1296124
ckpt进程的trace文件中报如下错误

Oracle Database 11g Enterprise Edition Release 11.2.0.2.0 - 64bit Production
With the Partitioning, Real Application Clusters, Automatic Storage Management, OLAP,
Data Mining and Real Application Testing options
ORACLE_HOME = /oradb/11.2.0/db
System name:	AIX
Node name:	offondb2
Release:	1
Version:	6
Machine:	00CC83664C00
Instance name: offon2
Redo thread mounted by this instance: 2
Oracle process number: 20
Unix process pid: 19660878, image: oracle@offondb2 (CKPT)


*** 2012-10-26 13:25:00.971
  1: 9430ms (rw) file: kct.c line: 7800 count: 13 total: 26874ms time: 1296124
  2: 1777ms (rw) file: krse.c line: 1800 count: 164 total: 122140ms time: 364176
  3: 1450ms (rw) file: kct.c line: 1011 count: 1 total: 1450ms time: 1594117
  4: 1230ms (rw) file: kcrf.c line: 10012 count: 135 total: 90995ms time: 2630737
  5: 1173ms (ro) file: kcrr.c line: 3525 count: 13 total: 8842ms time: 3645916
  6: 890ms (rw) file: kcrf.c line: 9959 count: 8 total: 4812ms time: 3578222
  7: 830ms (ro) file: kcf.c line: 5306 count: 1 total: 830ms time: 1594116
  8: 677ms (rw) file: kcv.c line: 11783 count: 8 total: 4499ms time: 416869
Control file enqueue hold time tracking dump at time: 2092019

*** 2012-10-26 15:25:14.789
  1: 9430ms (rw) file: kct.c line: 7800 count: 13 total: 26874ms time: 1296124
  2: 1777ms (rw) file: krse.c line: 1800 count: 165 total: 122832ms time: 364176
  3: 1450ms (rw) file: kct.c line: 1011 count: 1 total: 1450ms time: 1594117
  4: 1230ms (rw) file: kcrf.c line: 10012 count: 135 total: 90995ms time: 2630737
  5: 1173ms (ro) file: kcrr.c line: 3525 count: 13 total: 8842ms time: 3645916
  6: 890ms (rw) file: kcrf.c line: 9959 count: 8 total: 4812ms time: 3578222
  7: 830ms (ro) file: kcf.c line: 5306 count: 1 total: 830ms time: 1594116
  8: 677ms (rw) file: kcv.c line: 11783 count: 8 total: 4499ms time: 416869

原因分析并解决

New controlfile enqueue hold time tracking statistics have been added in 11.2 to 
aid diagnosis of controlfile transaction related performance related issues.

To disable the trace set _controlfile_enqueue_holding_time_tracking_size to 0:

- spfile
alter system set "_controlfile_enqueue_holding_time_tracking_size"=0 scope=spfile;

- pfile
_controlfile_enqueue_holding_time_tracking_size=0

A database restart is required.

查询_controlfile_enqueue_holding_time_tracking_size

SQL> col name for a32
SQL> col value for a24
SQL> col description for a70
SQL> set linesize 150
SQL> select a.ksppinm name,b.ksppstvl value,a.ksppdesc description
  2    from x$ksppi a,x$ksppcv b
  3   where a.inst_id = USERENV ('Instance')
  4     and b.inst_id = USERENV ('Instance')
  5     and a.indx = b.indx
  6     and upper(a.ksppinm) LIKE upper('%&param%')
  7  order by name
  8  /
Enter value for param: _controlfile_enqueue_holding_time_tracking_size
old   6:    and upper(a.ksppinm) LIKE upper('%&param%')
new   6:    and upper(a.ksppinm) LIKE upper('%_controlfile_enqueue_holding_time_tracking_size%')
</strong>
NAME                             VALUE      DESCRIPTION
-------------------------------- ---------- ------------------------------------------------
_controlfile_enqueue_holding_tim 10         control file enqueue holding time tracking size
e_tracking_size

补充MOS说明[791417.1]

New controlfile enqueue hold time tracking statistics have been added in 11.2 to aid 
diagnosis of controlfile transaction related performance related issues:

Control File Enqueue AWR Statistics:
max cf enq hold time - The maximum amount of time in milliseconds a client has held the control file enqueue.
total cf enq hold time - The total amount of time in milliseconds all clients have held the control file enqueue.
total number of cf enq holders - The total number of times clients have held the control file enqueue.

Periodically, the CKPT process dumps statistics for the top N control file enqueue holders. 
N defaults to 10, but can be modified with the static hidden 
parameter: _controlfile_enqueue_holding_time_tracking_size.The dump looks like the following:

Preface: "Control file enqueue hold time tracking dump at time: [relative time]".
a. Time the client has held the control file enqueue.
b. Type of client's control file enqueue transaction - rw or ro.
c. File name where the client obtained control file enqueue.
d. Line number where the client obtained control file enqueue.
e. Number of times the client has held the control file enqueue since it became a member of the top N.
f. Total time the client has held the control file in all those times from [e].
g. Relative time the client obtained the control file enqueue from [a].