在Oracle9i中,如何监视索引并清除监视信息:2012年Oracle考试:综合辅导-百考试题网

对于DML操作来说，索引对于数据库是一个性能负担.如果索引没有被有效的使用,那么其存在性就值得从新考虑.

1. 从Oracle9i开始,Oracle允许你监视索引的使用:

SQL> connect scott/tiger@conner
Connected to Oracle9i Enterprise Edition Release 9.2.0.4.0
Connected as scott
SQL> 0select index_name from user_indexes.
INDEX_NAME
------------------------------
PK_DEPT
PK_EMP
开始监视pk_dept索引:
SQL> alter index pk_dept monitoring usage.
Index altered
在此过程中,如果查询使用索引,将会记录下来:
SQL> 0select * from dept where deptno=10.
DEPTNO DNAME LOC
------ -------------- -------------
10 ACCOUNTING NEW YORK
停止监视:
SQL> alter index pk_dept nomonitoring usage.
Index altered
查询索引使用情况,YES表示在监视过程中索引被使用到:
SQL> 0select * from v$object_usage.
INDEX_NAME TABLE_NAME MONITORING USED START_MONITORING END_MONITORING
----------------- ------------------ ---------- ---- --------------------------------------
PK_DEPT DEPT NO YES 10/28/2004 10:55:19 10/28/2004 10:55:47
SQL>

2.Oracle9i的Bug

在9205之前，如果你不慎监控了SYS.I_OBJAUTH1索引，并且不幸在重起数据库之前没有停止它，那么你的数据库将会无法启动，并且不会给出任何错误信息。以下这条简单的语句可以轻易再现这个问题:ALTER INDEX SYS.I_OBJAUTH1 MONITORING USAGE 如果你有了足够好的备份(严重警告，请不要拿你的生产数据库进行测试)，你可以尝试一下:

[oracle@jumper oradata]$ sqlplus "/ as sysdba"
SQL*Plus: Release 9.2.0.4.0 - Production on Sat Dec 4 10:09:30 2004
Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved.
Connected to:
Oracle9i Enterprise Edition Release 9.2.0.4.0 - Production
With the Partitioning option
JServer Release 9.2.0.4.0 - Production
SQL> alter index SYS.I_OBJAUTH1 monitoring usage .
Index altered.
SQL> shutdown immediate.
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup
ORACLE instance started.
Total System Global Area 80811208 bytes
Fixed Size 451784 bytes
Variable Size 37748736 bytes
Database Buffers 41943040 bytes
Redo Buffers 667648 bytes
Database mounted.

此时，数据库挂起，而且不会有任何提示，在alert.log文件中，你可以看到:

[oracle@jumper bdump]$ tail -f alert_conner.log
Completed: ALTER DATABASE MOUNT
Sat Dec 4 10:09:49 2004ALTER DATABASE OPENSat Dec 4 10:09:49 2004
LGWR: Primary database is in CLUSTER CONSISTENT mode
Thread 1 opened at log sequence 54
Current log# 2 seq# 54 mem# 0: /opt/oracle/oradata/conner/redo02.log
Successful open of redo thread 1.
Sat Dec 4 10:09:49 2004
SMON: enabling cache recovery
Sat Dec 4 10:10:33 2004
Restarting dead background process QMN0
QMN0 started with pid=9