1、冗余索引的弊端   

大量冗余和无用的索引导致整个数据库性能低下，耗用了大量的CPU与I/O开销，具体表现如下:      

a、耗用大量的存储空间(索引段的维护与管理)      

b、增加了DML完成的时间      

c、耗用大量统计信息(索引)收集的时间      

d、结构性验证时间      

f、增加了恢复所需的时间

2、单个索引监控        

a、对于单个索引的监控，可以使用下面的命令来完成          

alter index <INDEX_NAME> monitoring usage;      

b、关闭索引监控         

alter index <INDEX_NAME> nomonitoring usage;      

c、观察监控结果(查询v$object_usage视图)         

select * from v$object_usage

3、schema级别索引监控(不含SYS用户)

a、直接执行脚本来开启索引监控

robin@SZDB:~/dba_scripts/custom/sql> more idx_monitor_on.sql

SET HEADING OFF  FEEDBACK OFF  TERMOUT OFF  ECHO OFF;

SET PAGESIZE 0;

SPOOL /tmp/mnt_idx.sql

SELECT 'ALTER INDEX ' || owner || '.' || index_name || ' MONITORING USAGE;'  FROM dba_indexes 

WHERE owner IN (SELECT username FROM dba_users WHERE account_status = 'OPEN')      

AND owner NOT IN ('SYS', 'SYSTEM', 'PERFSTAT', 'MGMT_VIEW', 'MONITOR', 'SYSMAN', 'DBSNMP');

SPOOL OFF;

b、禁用索引监控

robin@SZDB:~/dba_scripts/custom/sql> more idx_monitor_off.sql

SET HEADING OFF  FEEDBACK OFF  TERMOUT OFF  ECHO OFF;

SET PAGESIZE 0;

SPOOL /tmp/un_mnt_idx.sql

SELECT 'ALTER INDEX ' || owner || '.' || index_name || ' NOMONITORING USAGE;'  FROM dba_indexes 

WHERE owner IN (SELECT username  FROM dba_users  WHERE account_status = 'OPEN')      

AND owner NOT IN ('SYS', 'SYSTEM', 'PERFSTAT', 'MGMT_VIEW', 'MONITOR', 'SYSMAN', 'DBSNMP');

SPOOL OFF;

c、查看索引监控结果

set linesize 190

SELECT u.name owner,      

io.name index_name,      

t.name table_name,      

DECODE (BITAND (i.flags, 65536), 0, 'NO', 'YES') monitoring,      

DECODE (BITAND (ou.flags, 1), 0, 'NO', 'YES') used,      

ou.start_monitoring start_monitoring,      

ou.end_monitoring end_monitoring 

FROM sys.user$ u,       sys.obj$ io,       sys.obj$ t,       sys.ind$ i,       sys.object_usage ou

WHERE i.obj# = ou.obj# AND io.obj# = ou.obj# AND t.obj# = i.bo#

AND u.user# = io.owner#      

AND u.name=decode(upper('&input_owner'),'ALL',u.name,upper('&input_owner'));