诡异dblink问题解决

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标题:诡异dblink问题解决

作者:惜分飞©版权所有[未经本人同意,不得以任何形式转载,否则有进一步追究法律责任的权利.]

一、诡异dblink起源
今天开发拿过来一条sql,说有诡异现象,sql如下

INSERT INTO TAB_CS_CALLLOG
select c.user_logon,/*工号*/c.user_name,/*姓名*/a.call_id,/*通话id*/
      a.caller_nbr,/*主叫号码*/a.called_nbr,/*被叫号码*/d.start_time,/*呼入时间*/
      b.call_time,/*接听时间*/b.end_time,/*结束时间*/b.call_dura,/*时长*/
      to_number(b.call_time-d.start_time)*24*3600,/*等待时长*/
      decode(c.user_logon,null,0,1),/*类型*/
case
        when substr (a.CALLED_NBR,7, 2) = '00'
          then '广东移动'
        when substr (a.CALLED_NBR,7, 2) = '01'
          then '浙江移动'
        when substr (a.CALLED_NBR,7, 2) = '02'
          then '福建'
        when substr (a.CALLED_NBR,7, 2) = '03'
          then '四川'
        when substr (a.CALLED_NBR,7, 2) = '04'
          then '河南'
        when substr (a.CALLED_NBR,7, 2) = '05'
          then '湖北'
        when substr (a.CALLED_NBR,7, 2) = '06'
          then '北京CSIP'
        when substr (a.CALLED_NBR,7, 2) = '07'
          then '陕西'
        when substr (a.CALLED_NBR,7, 2) = '08'
          then '吉林'
        when substr (a.CALLED_NBR,7, 2) = '09'
          then '江西'
        when substr (a.CALLED_NBR,7, 2) = '10'
          then '宁夏'
        when substr (a.CALLED_NBR,7, 2) = '11'
          then '太原'
        when substr (a.CALLED_NBR,7, 2) = '12'
          then '江苏移动'
        when substr (a.CALLED_NBR,7, 2) = '13'
          then 'e掌管'
        when substr (a.CALLED_NBR,7, 2) = '15'
          then 'e多商'
        when substr (a.CALLED_NBR,7, 2) = '18'
          then '江苏联通'
      end 区域
from cscnew.a@cs a,cscnew.b@cs b,cscnew.c@cs c,cscnew.d@cs d
where a.call_serial=b.call_serial(+)
and b.call_serial=d.call_serial(+)
and b.user_id=c.user_id(+)
and substr(a.CALLED_NBR,1, 6) = '951654'
and  length (a.CALLED_NBR) = 15
and b.fail_reason is null
and a.end_time>=to_date('20110822000000','yyyymmddhh24miss')
and a.end_time<to_date('20110823000000','yyyymmddhh24miss');

然后我进行了测试,证实了她所说的诡异:
1、直接执行select语句需要1.7S左右,但是加上insert inot后,执行时间需要6分钟
2、直接select结果集为602条,加上insert into后,结果集为598条(少4条),如果直接执行select,除掉and b.fail_reason is null限制条件也刚好602条

二、查询相关资料,得到dblink的一些解释
1、dblink执行有两种方式,一种是在远处数据库执行完,然后结果返回,另一种是把远程的表下载到本来,然后执行
2、如果把远程的表下载到本地,空值或者null可能会发生变化(怀疑是空值转化为null,未证实)

三、根据这些解释,进行猜想
1、只执行select的时候,应该是在远程执行完,传输结果回来;而执行insert into的时候,是把远程的表全部下载到本地,然后执行出结果,而数据量本身比较大,所以比较慢
2、在把表从远程下载到本地的过程中,fail_reason 列的null值可以发生了变化,或者空值变为了null,所以数据多了4条

四、事实证明猜想
1、查询远程表大小,发现a表50m,b表400m,c表10m,d表100m左右,传输过来需要一定的时间
2、既然猜测是由于要把表传输到本地而导致这样的结果产生,那么处理方法就是让程序在远程计算出结果,然后传输到本地,查询了一些资料,上面说insert into会导致driving_site提示无效,那么我想到一个用视图的办法解决这个问题:在目标端建立一个关于本查询中无参数的视图,然后在本地通过dblink调用视图,这样总该先在远程执行出结果传输到本地了吧。
2.1)建立目标端视图

create or replace view v_tab
select c.user_logon,/*工号*/c.user_name,/*姓名*/a.call_id,/*通话id*/
      a.caller_nbr,/*主叫号码*/a.called_nbr,/*被叫号码*/d.start_time,/*呼入时间*/
      b.call_time,/*接听时间*/b.end_time,/*结束时间*/b.call_dura,/*时长*/
      to_number(b.call_time-d.start_time)*24*3600,/*等待时长*/
      decode(c.user_logon,null,0,1),/*类型*/
case
        when substr (a.CALLED_NBR,7, 2) = '00'
          then '广东移动'
        when substr (a.CALLED_NBR,7, 2) = '01'
          then '浙江移动'
        when substr (a.CALLED_NBR,7, 2) = '02'
          then '福建'
        when substr (a.CALLED_NBR,7, 2) = '03'
          then '四川'
        when substr (a.CALLED_NBR,7, 2) = '04'
          then '河南'
        when substr (a.CALLED_NBR,7, 2) = '05'
          then '湖北'
        when substr (a.CALLED_NBR,7, 2) = '06'
          then '北京CSIP'
        when substr (a.CALLED_NBR,7, 2) = '07'
          then '陕西'
        when substr (a.CALLED_NBR,7, 2) = '08'
          then '吉林'
        when substr (a.CALLED_NBR,7, 2) = '09'
          then '江西'
        when substr (a.CALLED_NBR,7, 2) = '10'
          then '宁夏'
        when substr (a.CALLED_NBR,7, 2) = '11'
          then '太原'
        when substr (a.CALLED_NBR,7, 2) = '12'
          then '江苏移动'
        when substr (a.CALLED_NBR,7, 2) = '13'
          then 'e掌管'
        when substr (a.CALLED_NBR,7, 2) = '15'
          then 'e多商'
        when substr (a.CALLED_NBR,7, 2) = '18'
          then '江苏联通'
      end 区域
from cscnew.a a,cscnew.b b,cscnew.c c,cscnew.d d
where a.call_serial=b.call_serial(+)
and b.call_serial=d.call_serial(+)
and b.user_id=c.user_id(+)
and substr(a.CALLED_NBR,1, 6) = '951654'
and  length (a.CALLED_NBR) = 15
and b.fail_reason is null

2.2)本地调用远程视图

INSERT INTO TAB_CS_CALLLOG
select * from v_tab@cs a where 
a.end_time>=to_date('20110822000000','yyyymmddhh24miss')
and a.end_time<to_date('20110823000000','yyyymmddhh24miss');

2.3)执行结果2.3S完成数据插入,而且条数也是598条,证明我的猜想是正确的,更重要的是解决了今天这个让人疑惑的问题

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诡异dblink问题解决》有 1 条评论

  1. gull_y 说:

    细节方面的问题确实值得深入思考,确实思维方法值得学习。

      [引用]  [回复]

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