Oracle索引监控(monitor index)

x635505360 2013-03-22 05:57:43

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了查询性能。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耗用了大量的存储空间，导致DML性能低下。Oracle/" target=_blank>Oracle 提供了索引监控特性来初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 <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)
[sql]
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;

--> Author : Robinson
--> Blog : http://blog.csdn.net/robinson_0612

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
[sql]
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(初略值)
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初略值

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