Oracle性能优化有时就这么简单_index
性能优化有时就这么简单
一、概述
最近有一个系统（aix6.1+Oracle10.2.0.5 RAC）CPU每五分钟就达到百分之百，这个系统是监控系统，针对所有运行系统每五分钟取数，所以之前也没太在意， 其实在年前就有过这种情况，只是把执行频繁的语句发送给项目组，有针对系统运行环境调整了一下SGA等大小，只是不告警了（cpu使用超过百分之九十就告警），也就没管。可这几天有出现该问题，还是继续将执行频繁的sql发送给项目组，由于所有受监控的系统都会每五分钟向该系统发数，也就理所当然的认为系统就这个特点，也就没理会。可是，这两天，告警短信也每五分钟就发送一次，随之的恢复短信，自己看着不烦，领导看着也烦啊，那就看看吧（虽然对sql语句不感冒吧）
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二、 处理过程
通过提取一段时间内的AWR，发现下面这条语句执行次数最频繁，当然也是消耗cpu资源最多的。
SELECT V1400, H, L, A, to_char(HTIME, 'yyyy-mm-dd hh24:mi:ss'), to_char(LTIME, 'yyyy-mm-dd hh24:mi:ss') FROM XXXDBA.ORACLETABLEAVAILABLE WHERE RESOURCEID = :1 AND TIME = to_date(:2, 'yyyy-mm-dd')
第一眼看去有绑定变量，而且截取几个时间段的AWR发现每次执行的语句列名也不完全相同，就想，让项目组的人去看吧。闲来无事，就查看了一下该表的信息
SQL> desc XXXDBA.ORACLETABLEAVAILABLE
Name Null? Type
---------------------------------------
RESOURCEID NOT NULL VARCHAR2(128)
TIME NOT NULL DATE
V0000 NUMBER
V0005 NUMBER
V0010 NUMBER
V0015 NUMBER
V0020 NUMBER
V0025 NUMBER
V0030 NUMBER
V0035 NUMBER
V0040 NUMBER
………………………………..
V2355 NUMBER
H NUMBER
L NUMBER
A NUMBER
HTIME DATE
LTIME DATE
第一反应是感觉这个表会不会定时或者根据条件更新列啊，先不管了，看一下执行计划再说，发现执行一次竟然那么长时间，而且走的全表扫描
SQL> explain plan for SELECT V0800,H,L,A,to_char(HTIME,'yyyy-mm-dd hh24:mi:ss'),to_char(LTIME,'yyyy-mm-dd hh24:mi:ss') FROM XXXDBA.ORACLETABLEAVAILABLE WHERE RESOURCEID = :1 AND TIME = to_date(:2,'yyyy-mm-dd');
Explained.
SQL> select * from table(dbms_xplan.display);
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Plan hash value: 1457290298
-----------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-----------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 65 | 18311 (1)| 00:03:40 |
|* 1 | TABLE ACCESS FULL| ORACLETABLEAVAILABLE | 1 | 65 | 18311 (1)| 00:03:40 |
-----------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("RESOURCEID"=:1 AND "TIME"=TO_DATE(:2,'yyyy-mm-dd'))
13 rows selected.
查看该表行数
SQL> select count(*) from XXXDBA.ORACLETABLEAVAILABLE;
COUNT(*)
----------
326796
查看是否有相关索引，竟然没有索引，按理说该表不算太大，但执行次数太多，加个索引会快些吧
SQL> select owner,index_name,index_type,table_name from dba_indexes where table_name='ORACLETABLEAVAILABLE';
no rows selected
通过询问项目组人员，得知，该表收集受监听系统时间点数据，更做相应更新操作，列名不变，查询语句中条件语句列RESOURCEID是唯一的，建议项目组添加索引，索引信息如下
SQL> select owner,index_name,index_type,table_name from dba_indexes where table_name='ORACLETABLEAVAILABLE';
OWNER INDEX_NAME INDEX_TYPE TABLE_NAME
------------------------------ ------------------------------ --------------------------- ------------------------------
XXXDBA P_ORACLETABLEAVAILABLE NORMAL ORACLETABLEAVAILABLE
SQL> select dbms_metadata.get_ddl('INDEX','P_ORACLETABLEAVAILABLE','XXXDBA') from dual;
DBMS_METADATA.GET_DDL('INDEX','P_ORACLETABLEAVAILABLE','XXXDBA')
--------------------------------------------------------------------------------------------------------------------
CREATE UNIQUE INDEX "XXXDBA"."P_ORACLETABLEAVAILABLE" ON "XXXDBA"."ORACLETABLEAVAILABLE" ("RESOURCEID", "TIME")
PCTFREE 10 INITRANS 2 MAXTRANS 255 COMPUTE STATISTICS
STORAGE(INITIAL 131072 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645
PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1 BUFFER_POOL DEFAULT)
TABLESPACE "PERFORMANCE"
再次查看执行计划，这速度，杠杠的
SQL> explain plan for SELECT V0900,H,L,A,to_char(HTIME,'yyyy-mm-dd hh24:mi:ss'),to_char(LTIME,'yyyy-mm-dd hh24:mi:ss')
2 FROM XXXDBA.ORACLETABLEAVAILABLE
3 WHERE RESOURCEID = :1 AND TIME = to_date(:2,'yyyy-mm-dd')
4 ;
Explained.
SQL> select * from table(dbms_xplan.display);
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Plan hash value: 1279632247
-----------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-----------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 65 | 3 (0)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| ORACLETABLEAVAILABLE | 1 | 65 | 3 (0)| 00:00:01 |
|* 2 | INDEX UNIQUE SCAN | P_ORACLETABLEAVAILABLE | 1 | | 2 (0)| 00:00:01 |
-----------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("RESOURCEID"=:1 AND "TIME"=TO_DATE(:2,'yyyy-mm-dd'))
14 rows selected.