索引监控

索引监控

在某个OLTP系统中某张表上建立了10个索引，由于不确定索引是否有在各程序中被使用，不能随意删除，因此，需要监控已有的索引是否在使用，

官方文档描述：

Monitoring Index Usage

Oracle Database provides a means of monitoring indexes to determine whether they are being used. If an index is not being used, then it can be dropped, eliminating unnecessary statement overhead.

To start monitoring the usage of an index, issue this statement:

ALTER INDEX index MONITORING USAGE; //开启索引监控

Later, issue the following statement to stop the monitoring:

ALTER INDEX index NOMONITORING USAGE; //关闭索引监控


The view V$OBJECT_USAGE can be queried for the index being monitored to see if the index has been used. The view contains a USED column whose value is YES or NO, depending upon if the index has been used within the time period being monitored. The view also contains the start and stop times of the monitoring period, and a MONITORING column (YES/NO) to indicate if usage monitoring is currently active.

Each time that you specify MONITORING USAGE, the V$OBJECT_USAGE view is reset for the specified index. The previous usage information is cleared or reset, and a new start time is recorded. When you specify NOMONITORING USAGE, no further monitoring is performed, and the end time is recorded for the monitoring period. Until the next ALTER INDEX...MONITORING USAGE statement is issued, the view information is left unchanged.

开启索引监控后，可以从v$object_usage中查询到数据（即使索引还没有被使用），START_MONITORING 字段会写入开始监控的时间；当某条SQL使用了相关的索引以后，其“USED”字段就会更新为’YES‘。监控索引结束后最好关闭监控，以提高效率。

注意：v$object_usage 要去每个USERS 中查询，即使用SYS权限开启的其他USER索引的监控，也无法从SYS用户的V$OBJECT_USAGE 中插到相关的记录。 下面有验证

实验： 测试一个索引

[oracle@tyger ~]$ sqlplus / as sysdba


SQL*Plus: Release 10.2.0.1.0 - Production on Fri Mar 28 16:19:01 2014


Copyright (c) 1982, 2005, Oracle. All rights reserved.




Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options


SYS@ORCL>create user tyger identified by tyger; // 创建测试用户 tyger


User created.


SYS@ORCL>grant connect,resource to tyger; // 赋予tyger connect，resource 权限


Grant succeeded.


SYS@ORCL>grant select on dba_objects to tyger; // 授予 dba_objects 查询权限给 tyger


Grant succeeded.


SYS@ORCL>conn tyger/tyger
Connected.
TYGER@ORCL>create table test_monitor as select * from dba_objects; // 创建测试表


Table created.


TYGER@ORCL>select * from user_indexes; // 查看当前用户下的索引


no rows selected


TYGER@ORCL>create index test_monitor_idx on test_monitor(object_id); // 基于 object_id 字段创建索引


Index created.

TYGER@ORCL>col INDEX_NAME for a20
TYGER@ORCL>col TABLE_NAME for a20
TYGER@ORCL>col TABLE_OWNER for a20
TYGER@ORCL>l
1 select index_name,table_name,table_owner
2* from user_indexes
TYGER@ORCL>/ // 查看当前用户下的索引

INDEX_NAME TABLE_NAME TABLE_OWNER
-------------------- -------------------- --------------------
TEST_MONITOR_IDX TEST_MONITOR TYGER


TYGER@ORCL>

TYGER@ORCL>alter index TEST_MONITOR_IDX monitoring usage; // 开启索引监控


Index altered.


TYGER@ORCL>select * from v$object_usage; // 查看视图 object_usage 索引监控和使用情况


INDEX_NAME TABLE_NAME MON USE START_MONITORING
-------------------- -------------------- --- --- -------------------
END_MONITORING
-------------------
TEST_MONITOR_IDX TEST_MONITOR YES NO 03/28/2014 16:22:46 // MONITORING 为 'YES' 代表已经监控
// USAGE 为 ’NO‘ 代表索引未被使用

TYGER@ORCL>conn / as sysdba
Connected.
SYS@ORCL>
SYS@ORCL>select * from v$object_usage; // 无法从SYS用户的V$OBJECT_USAGE 中插到相关的记录


no rows selected


TYGER@ORCL>set autotrace on // 开启自动跟踪
SP2-0618: Cannot find the Session Identifier. Check PLUSTRACE role is enabled // 出现这个错误，暂时可以略过，不影响接下来的实验
SP2-0611: Error enabling STATISTICS report
TYGER@ORCL>select * from TEST_MONITOR where object_id=111;


OWNER
------------------------------
OBJECT_NAME
--------------------------------------------------------------------------------
SUBOBJECT_NAME OBJECT_ID DATA_OBJECT_ID OBJECT_TYPE
------------------------------ ---------- -------------- -------------------
CREATED LAST_DDL_ TIMESTAMP STATUS T G S
--------- --------- ------------------- ------- - - -
SYS
I_ARGUMENT1
111 111 INDEX
30-JUN-05 30-JUN-05 2005-06-30:19:10:18 VALID N N N



Execution Plan
----------------------------------------------------------
Plan hash value: 2240611133


--------------------------------------------------------------------------------
----------------


| Id | Operation | Name | Rows | Bytes | Cost (%
CPU)| Time |


--------------------------------------------------------------------------------
----------------


| 0 | SELECT STATEMENT | | 1 | 177 | 2
(0)| 00:00:01 |


| 1 | TABLE ACCESS BY INDEX ROWID| TEST_MONITOR | 1 | 177 | 2
(0)| 00:00:01 |


|* 2 | INDEX RANGE SCAN | TEST_MONITOR_IDX | 1 | | 1 // 上面执行的语句 走的是索引 TEST_MONITOR_IDX
(0)| 00:00:01 |


--------------------------------------------------------------------------------
----------------




Predicate Information (identified by operation id):
---------------------------------------------------


2 - access("OBJECT_ID"=111)


Note
-----
- dynamic sampling used for this statement


TYGER@ORCL>select * from v$object_usage;


INDEX_NAME TABLE_NAME MON USE START_MONITORING
-------------------- -------------------- --- --- -------------------
END_MONITORING
-------------------
TEST_MONITOR_IDX TEST_MONITOR YES YES 03/28/2014 16:22:46 // MONITORING 为 'YES' 代表已经监控
// USAGE 为 ’YES‘ 代表索引已经被使用








Execution Plan
----------------------------------------------------------
ERROR:
ORA-01039: insufficient privileges on underlying objects of the view




SP2-0612: Error generating AUTOTRACE EXPLAIN report
TYGER@ORCL>set autotrace off;
TYGER@ORCL>