由于物化视图定义为on commit导致update更新基表慢的解决方案

由于物化视图定义为on commit导致update更新基表慢的解决方案
以下是模拟和解决测试过程：


(模拟update慢的过程)
1、首先基于基表创建物化视图日志:
create materialized view log on scott.emp with rowid;


2、首先基于scott用户下emp创建物化视图：


create materialized view mv_emp


REFRESH FAST on commit


as


select * from scott.emp;


3、通过oracle 10046 查看update语句执行过程:
(1)sql>alter session set sql_trace=true;
(2)sql>alter session set tracefile_identifier='lzq';
(3)sql>alter session set events '10046 trace name context forever, level 1';
(4)sql>update scott.emp set sal=1450 where empno=7934;
(5)sql>alter session set events '10046 trace name context off';
(6)sql>show parameter user_dump_dest
(7)cd 到user_dump_dest查看trace文件被标识为lzq的trace 文件.
(8)格式化trace文件方便查看，tkprof prod2_ora_8623_lzq.trc prod2_ora_8623_lzq.out
(9)查看生成的prod2_ora_8623_lzq.out文件并查找跟物化视图mv_emp执行相关的信息见如下：
(生产环境中update一条语句真正执行的时间为1分多，而其中此处merger into "SCOTT"."MV_EMP" 占了1分左右
，而物化视图真正是给日报、月报、年报来用的跟客户沟通不用更新基表的时候就立即更新物化视图，物化视图
可以抛弃on commit时候就刷新，可以采取定时更新即可，从而可以避免update更新基表慢的问题。)


MERGE INTO "SCOTT"."MV_EMP" "SNA$" USING (SELECT CURRENT$."EMPNO",
  CURRENT$."ENAME",CURRENT$."JOB",CURRENT$."MGR",CURRENT$."HIREDATE",
  CURRENT$."SAL",CURRENT$."COMM",CURRENT$."DEPTNO" FROM (SELECT "EMP"."EMPNO" 
  "EMPNO","EMP"."ENAME" "ENAME","EMP"."JOB" "JOB","EMP"."MGR" "MGR",
  "EMP"."HIREDATE" "HIREDATE","EMP"."SAL" "SAL","EMP"."COMM" "COMM",
  "EMP"."DEPTNO" "DEPTNO" FROM "EMP" "EMP") CURRENT$, (SELECT DISTINCT 
  MLOG$."EMPNO" FROM "SCOTT"."MLOG$_EMP" MLOG$ WHERE "XID$$" = :1      AND 
  ("DMLTYPE$$" != 'D')) LOG$ WHERE CURRENT$."EMPNO" = LOG$."EMPNO")"AV$" ON 
  ("SNA$"."EMPNO" = "AV$"."EMPNO") WHEN MATCHED THEN UPDATE  SET 
  "SNA$"."EMPNO" = "AV$"."EMPNO","SNA$"."ENAME" = "AV$"."ENAME","SNA$"."JOB" =
   "AV$"."JOB","SNA$"."MGR" = "AV$"."MGR","SNA$"."HIREDATE" = 
  "AV$"."HIREDATE","SNA$"."SAL" = "AV$"."SAL","SNA$"."COMM" = "AV$"."COMM",
  "SNA$"."DEPTNO" = "AV$"."DEPTNO" WHEN NOT MATCHED THEN INSERT  
  (SNA$."EMPNO",SNA$."ENAME",SNA$."JOB",SNA$."MGR",SNA$."HIREDATE",SNA$."SAL",
  SNA$."COMM",SNA$."DEPTNO") VALUES (AV$."EMPNO",AV$."ENAME",AV$."JOB",
  AV$."MGR",AV$."HIREDATE",AV$."SAL",AV$."COMM",AV$."DEPTNO")
   


call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        1      0.00       0.00          0          0          0           0
Execute      1      0.01       0.08          2         20          5           1
Fetch        0      0.00       0.00          0          0          0           0
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total        2      0.01       0.08          2         20          5           1


(模拟update慢的解决方案：)
1、首先删除之前创建的物化视图(先做个备份)
drop  MATERIALIZED VIEW mv_emp;


2、创建物化视图
CREATE MATERIALIZED VIEW mv_emp 
  AS SELECT * FROM scott.emp;


3、建立一个用来刷新物化视图的存储过程:


CREATE OR REPLACE PROCEDURE auto_refresh_mview_job_proc 
AS 
BEGIN 
  dbms_mview.REFRESH('mv_emp'); 
END; 


4、用ORACLE 10g的scheduler每天12:00和19:00定期刷新物化视图(时间可以根据需求定义)


BEGIN 
DBMS_SCHEDULER.CREATE_JOB( 
job_name => 'auot_refresh_mview_job', 
job_type => 'STORED_PROCEDURE', 
job_action => 'scott.auto_refresh_mview_job_proc', 
start_date => SYSDATE, 
repeat_interval => 'FREQ=DAILY; BYHOUR=12,19', 
enabled => TRUE, 
comments => 'Refresh materialized view mv_emp' 
); 
END; 


5、通过oracle 10046 查看update语句执行过程:
(1)sql>alter session set sql_trace=true;
(2)sql>alter session set tracefile_identifier='lzq';
(3)sql>alter session set events '10046 trace name context forever, level 1';
(4)sql>update scott.emp set sal=1450 where empno=7934;
(5)sql>alter session set events '10046 trace name context off';
(6)sql>show parameter user_dump_dest
(7)cd 到user_dump_dest查看trace文件被标识为lzq的trace 文件.
(8)格式化trace文件方便查看，tkprof prod2_ora_8623_lzq.trc prod2_ora_8623_lzq.out
(9)查看生成的prod2_ora_8623_lzq.out文件并查找报告中是否还存在MERGE INTO "SCOTT"."MV_EMP"更新物化视图的信息，
此时因为已经定时为定时刷新，从而可以提高update语句的时间，从而优化过程完成。