Oracle索引监控(monitor index)

Oracle索引监控(monitor index)

合理的为数据库表上创建战略性索引，可以极大程度的提高查询性能。但事实上日常中我们所创建的索引并非战略性索引，恰恰是大量冗余或是根本没有用到的索引，这些索引耗用了大量的存储空间，导致DML性能低下。Oracle
提供了索引监控特性来粗略判断未使用到的索引。本文描述如何使用Oracle 索引的监控。

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 monitoring usage;

b、关闭索引监控

alter index 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;

@/tmp/mnt_idx.sql;

SET HEADING ON FEEDBACK ON TERMOUT ON;

SET PAGESIZE 80;

SELECT index_name,

monitoring,

used,

start_monitoring,

end_monitoring

FROM v$object_usage;

ho rm -rf /tmp/mnt_idx.sql

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;

@/tmp/un_mnt_idx.sql;

SET HEADING ON FEEDBACK ON TERMOUT ON;

SET PAGESIZE 80;

SELECT index_name,

monitoring,

used,

start_monitoring,

end_monitoring

FROM v$object_usage;

ho rm -rf /tmp/un_mnt_idx.sql

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'));

4、演示索引监控

a、单个索引监控

-->演示环境

scott@CNMMBO> select * from v$version where
rownum<2;

BANNER

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

Oracle Database 10g Release 10.2.0.3.0 - 64bit Production

-->创建测试表

scott@CNMMBO> create table tb_emp as select * from
emp;

-->为测试表创建索引

scott@CNMMBO> create index i_tb_emp_empno on
tb_emp(empno);

-->收集统计信息

scott@CNMMBO> exec
dbms_stats.gather_table_stats('SCOTT','TB_EMP',cascade=>true);

-->查看索引信息

scott@CNMMBO> @idx_info

Enter value for owner: scott

Enter value for table_name: tb_emp

Table
Name
INDEX_NAME
CL_NAM
CL_POS STATUS
IDX_TYP
DSCD

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

TB_EMP
I_TB_EMP_EMPNO
EMPNO
1 VALID
NORMAL
ASC

-->查看索引使用情况

-->此时use列为NO，表明索引未被使用到

scott@CNMMBO>
@idx_usage_tb

Enter value for 1: tb_emp

Enter value for 2: all

Enter value for 2: all

Table
Name
INDEX_NAME
USE
START_MONITORING
END_MONITORING

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

TB_EMP
I_TB_EMP_EMPNO
NO 03/19/2013 17:43:49

-->实施即席查询

scott@CNMMBO> select empno,ename,job from tb_emp
where empno=7788;

EMPNO
ENAME
JOB

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

7788
SCOTT
ANALYST

-->再次查看时USE列已经为YES

scott@CNMMBO> @idx_usage_tb

Enter value for 1: tb_emp

Enter value for 2: all

Enter value for 2: all

Table
Name
INDEX_NAME
USE
START_MONITORING
END_MONITORING

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

TB_EMP
I_TB_EMP_EMPNO
YES 03/19/2013 17:43:49

-->禁用索引监控

scott@CNMMBO> alter index I_TB_EMP_EMPNO
nomonitoring usage;

Index altered.

b、schema级别的索引监控

-->切换到另外一个数据库cnbo1

scott@CNMMBO> conn goex_admin/xxxxx@cnbo1

Connected.

-->下面的查询表明没有表开启索引监控

goex_admin@CNBO1> @idx_usage;

no rows selected

-->开启索引监控

goex_admin@CNBO1> @idx_monitor_on

INDEX_NAME
MON USE
START_MONITORING
END_MONITORING

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

PK_AAH
YES NO 03/19/2013 17:48:32

IDX_GOAAE1
YES NO 03/19/2013 17:48:32

PK_GOAAT
YES NO 03/19/2013 17:48:32

PK_GOAACTL
YES NO 03/19/2013 17:48:32

.......
................

-->关闭索引监控

goex_admin@CNBO1> @idx_monitor_off

INDEX_NAME
MON USE
START_MONITORING
END_MONITORING

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

PK_GOARL
NO NO 03/19/2013 17:48:30
03/19/2013 17:50:02

IDX_GOAQU1
NO NO 03/19/2013 17:48:30
03/19/2013 17:50:02

IDX_GOAQU2
NO NO 03/19/2013 17:48:30
03/19/2013 17:50:02

-->连接到原来的db，查看曾经开启索引监控的使用情况

goex_admin@CNBO1> conn scott/tiger@cnmmbo

Connected.

goex_admin@CNMMBO> @idx_usage

Enter value for input_owner: GOEX_ADMIN

Enter value for input_owner: GOEX_ADMIN

OWNER
INDEX_NAME
Table
Name
MON USE
START_MONITORING
END_MONITORING

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

SCOTT
I_TB_EMP_EMPNO
TB_EMP
NO YES 03/19/2013 17:43:49 03/19/2013 17:46:04

GOEX_ADMIN
ACC_GRP_EXT_INFO_TBL_LOG_PK
ACC_GRP_EXT_INFO_TBL_LOG YES YES 02/22/2013
15:58:42

GOEX_ADMIN
IDX_TDCL_CONTRACT_NUM
TRADE_CLIENT_TBL
YES YES 02/22/2013 15:58:42

GOEX_ADMIN
IDX_TDCL_SETTLED_DATE
TRADE_CLIENT_TBL
YES YES 02/22/2013 15:58:42

GOEX_ADMIN
IDX_TDCL_ACC_NUM
TRADE_CLIENT_TBL
YES YES 02/22/2013 15:58:41

GOEX_ADMIN
IDX_TDCL_INSTRU_ID
TRADE_CLIENT_TBL
YES YES 02/22/2013 15:58:42

5、索引监控的建议与弊端

a、选择数据库高峰期实施索引监控，以及尽可能使用较长的监控周期来判断索引是否被使用

b、可以对特定时间段实施多次监控以判断索引的使用频率(粗略值)

c、索引监控在一定程度上耗用系统资源，一旦监控完毕后应即时关闭以避免其带来的额外开销

d、索引监控仅仅从索引的使用与否来描述索引使用，并未提供详细的索引使用频率，b点提到的方法也只是粗略值

（Oracle
监控索引的使用率
参见：http://blog.csdn.net/robinson_0612/article/details/8823133）

转自：http://www.2cto.com/database/201303/196854.html