[20180823]IMU与db link.txt

[20180823]imu与db link.txt

--//当使用db link查看远程表时,实际上会产生小小的日志.
--//当时如果与imu结合在一起,可以导致imu的失效.

1.环境:
scott@book> @ ver1
port_string                    version        banner
------------------------------ -------------- --------------------------------------------------------------------------------
x86_64/linux 2.4.xx            11.2.0.4.0     oracle database 11g enterprise edition release 11.2.0.4.0 - 64bit production

create  public database link loopback connect to scott identified by book using 'localhost:1521/book:dedicated';
create table deptx as select * from dept;

2.测试:
scott@book> @ &r/viewsess "imu commits"
name        statistic#      value        sid
----------- ---------- ---------- ----------
imu commits        374          0          1

scott@book> update deptx set dname=lower(dname) where deptno=10;
1 row updated.

scott@book> commit;
commit complete.

scott@book> @ &r/viewsess "imu commits"
name        statistic#      value        sid
----------- ---------- ---------- ----------
imu commits        374          1          1

--//可以发现当前数据库imu起作用的.

scott@book> @ &r/viewsess "imu commits"
name        statistic#      value        sid
----------- ---------- ---------- ----------
imu commits        374          0          1

scott@book> update deptx set dname=lower(dname) where deptno=10;
1 row updated.

scott@book> select sysdate from dual@loopback;
sysdate
-------------------
2018-08-22 09:04:00

scott@book> commit ;
commit complete.

scott@book> @ &r/viewsess "imu commits"
name        statistic#      value        sid
----------- ---------- ---------- ----------
imu commits        374          0          1

--//当是当执行dml时有dblink的语句,imu失效,回到原来的模式.

--//viewsess.sql脚本:
set verify off
column name format a70
select b.name, a.statistic#, a.value,a.sid
  from v$mystat a, v$statname b
 where lower(b.name) like lower('%&1%') and a.statistic# = b.statistic# ;
 --and a.value>0;