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索引可以加快查询的速度，但索引会占用许多存储空间，在插入和删除行的时候，索引还会引入额外的开销，因此确保索引得到有效利用是我们很关注的一个问题。在Oracle9i之前，要知道一个索引是否被使用是困难的，而Oracle 9i中提供了一个有效的监控方法：ALTER INDEX MONITORING USAGE。

这里我以一个已有的索引，来演示怎样监控其使用情况，演示之前，我们可以查询一下视图v$object_usage，看看有什么结果，如果以前没启用过该功能，则查询不到任何信息。

首先，针对已有的index，启用其监视功能：

alter index INDEX_DEPLOYEE_IS_SNZY monitoring usage;
alter index INDEX_DEPLOYEE_IS_UPDATE monitoring usage;
alter index INDEX_DEPLOYEE_IDCARD monitoring usage;
alter index INDEX_DEPLOYEE_SCHOOLID monitoring usage;
alter index INDEX_DEPLOYEE_BY_HAND monitoring usage;
alter index INDEX_DEPLOYEE_COUNTY monitoring usage;
alter index INDEX_DEPLOYEE_HJXZ monitoring usage;
alter index INDEX_DEPLOYEE_IS_FEE monitoring usage;
alter index INDEX_DEPLOYEE_LOWER monitoring usage;
alter index INDEX_DEPLOYEE_PROVINCE monitoring usage;
alter index INDEX_DEPLOYEE_SPE monitoring usage;
alter index INDEX_DEPLOYEE_STATUS monitoring usage;

然后查看视图v$object_usage，结果如下：

SQL> select * from v$object_usage;

INDEX_NAME                     TABLE_NAME   MONITORING USED START_MONITORING    END_MONITORING
------------------------------ ----------- ---------- ---- ------------------- -------------------
INDEX_DEPLOYEE_IS_SNZY          T_DEPLOYEE   YES        NO   12/10/2010 17:08:26
INDEX_DEPLOYEE_IS_UPDATE        T_DEPLOYEE   YES        NO   12/10/2010 17:08:26
INDEX_DEPLOYEE_IDCARD           T_DEPLOYEE   YES        NO   12/10/2010 17:08:26
INDEX_DEPLOYEE_SCHOOLID         T_DEPLOYEE   YES        NO 12/10/2010 17:08:26
INDEX_DEPLOYEE_BY_HAND          T_DEPLOYEE   YES        NO   12/10/2010 17:08:26
INDEX_DEPLOYEE_COUNTY           T_DEPLOYEE   YES        NO   12/10/2010 17:08:26
INDEX_DEPLOYEE_HJXZ             T_DEPLOYEE   YES        NO   12/10/2010 17:08:26
INDEX_DEPLOYEE_IS_FEE           T_DEPLOYEE   YES        NO   12/10/2010 17:08:26
INDEX_DEPLOYEE_LOWER            T_DEPLOYEE   YES        NO   12/10/2010 17:08:26
INDEX_DEPLOYEE_PROVINCE         T_DEPLOYEE   YES        NO   12/10/2010 17:08:26
INDEX_DEPLOYEE_SPE              T_DEPLOYEE   YES        NO   12/10/2010 17:08:26
INDEX_DEPLOYEE_STATUS           T_DEPLOYEE   YES        NO   12/10/2010 17:08:26

14 rows selected

然后通过查询SQL语句，使部分索引起作用，再查看该视图，结果如：

SQL> select * from v$object_usage;

INDEX_NAME                     TABLE_NAME   MONITORING USED START_MONITORING    END_MONITORING
------------------------------ ----------- ---------- ---- ------------------- -------------------
INDEX_DEPLOYEE_IS_SNZY          T_DEPLOYEE   YES        NO   12/10/2010 17:08:26
INDEX_DEPLOYEE_IS_UPDATE        T_DEPLOYEE   YES        NO   12/10/2010 17:08:26
INDEX_DEPLOYEE_IDCARD           T_DEPLOYEE   YES        YES   12/10/2010 17:08:26
INDEX_DEPLOYEE_SCHOOLID         T_DEPLOYEE   YES        YES 12/10/2010 17:08:26
INDEX_DEPLOYEE_BY_HAND          T_DEPLOYEE   YES        NO   12/10/2010 17:08:26
INDEX_DEPLOYEE_COUNTY           T_DEPLOYEE   YES        NO   12/10/2010 17:08:26
INDEX_DEPLOYEE_HJXZ             T_DEPLOYEE   YES        NO   12/10/2010 17:08:26
INDEX_DEPLOYEE_IS_FEE           T_DEPLOYEE   YES        NO   12/10/2010 17:08:26
INDEX_DEPLOYEE_LOWER            T_DEPLOYEE   YES        NO   12/10/2010 17:08:26
INDEX_DEPLOYEE_PROVINCE         T_DEPLOYEE   YES        NO   12/10/2010 17:08:26
INDEX_DEPLOYEE_SPE              T_DEPLOYEE   YES        NO   12/10/2010 17:08:26
INDEX_DEPLOYEE_STATUS           T_DEPLOYEE   YES        NO   12/10/2010 17:08:26

14 rows selected

若不再需要监控索引使用情况时，只需要执行如下语句取消监控即可：

alter index INDEX_DEPLOYEE_IS_SNZY nomonitoring usage;
alter index INDEX_DEPLOYEE_IS_UPDATE nomonitoring usage;
alter index INDEX_DEPLOYEE_IDCARD nomonitoring usage;
alter index INDEX_DEPLOYEE_SCHOOLID nomonitoring usage;
alter index INDEX_DEPLOYEE_BY_HAND nomonitoring usage;
alter index INDEX_DEPLOYEE_COUNTY nomonitoring usage;
alter index INDEX_DEPLOYEE_HJXZ nomonitoring usage;
alter index INDEX_DEPLOYEE_IS_FEE nomonitoring usage;
alter index INDEX_DEPLOYEE_LOWER nomonitoring usage;
alter index INDEX_DEPLOYEE_PROVINCE nomonitoring usage;
alter index INDEX_DEPLOYEE_SPE nomonitoring usage;
alter index INDEX_DEPLOYEE_STATUS nomonitoring usage;

v$object_usage视图解释

从上面的例子中我们可以看出，索引的监视信息都是存在在v$objec_usage视图中，该视图的定义如下：

create or replace view sys.v$object_usage
(index_name, table_name, monitoring, used, start_monitoring, end_monitoring)
as
select io.name, t.name,
       decode(bitand(i.flags, 65536), 0, 'NO', 'YES'),
       decode(bitand(ou.flags, 1), 0, 'NO', 'YES'),
       ou.start_monitoring,
       ou.end_monitoring
from sys.obj$ io, sys.obj$ t, sys.ind$ i, sys.object_usage ou
where io.owner# = userenv('SCHEMAID')
and i.obj# = ou.obj#
and io.obj# = ou.obj#
and t.obj# = i.bo#

下面是该视图列的描述：
INDEX_NAME: sys.obj$.name 中的索引名字
TABLE_NAME: sys.obj$obj$name 中的表名
MONITORING: YES (索引正在被监控), NO (索引没有被监控)
USED: YES (索引已经被使用过), NO (索引没有被使用过)
START_MONITORING: 开始监控的时间
END_MONITORING: 结束监控的时间
所有被使用过至少一次的索引都可以被监控并显示到这个视图中。

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【转】监控Index是否被使用过的方法

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