Oracle distributed query optimization statement

Copyright attribution: Tiankai Technology

This link: https://blog.csdn.net/dbs_service/article/details/102761510

Analysis:
As the optimizer can not determine or obtain statistics on the distal end of the table, so the original execution plan will take the default remote table (regardless of size) pulled way local reconnection execution, so if the remote table will be relatively large case slowly, like the above query takes more than one minute.

Original SQL statement:

Select
 Wb.*,
 (Select Wi.Nextarrivedate
    From Mbs7_Oms.Xs_Warearriveinfo@Dc.Moonbasadb.Com Wi
   Where Wi.Warecode = Wb.Warecode) As Nextarrivedate
  From Mbs7_Crm.Wi_Warebase@Dc.Moonbasadb.Com Wb                 ---这里远端表较大
 Inner Join (Select Wa.Stylecode, Max(Wa.Warecode) As Warecode
               From Mbs7_Crm.Wi_Warebase@Dc.Moonbasadb.Com Wa
              Inner Join (Select Stylecode
                           From Dc_Support.Kh_Visitpage Vis
                          Where Vis.Cuscode = :B1
                            And Vis.Addtime >= Trunc(Sysdate - 31)
                            And Vis.Addtime < Trunc(Sysdate - 30)
                            And Rownum <= 5
                          Order By Addtime Desc) Vis
                 On Wa.Stylecode = Vis.Stylecode
              Group By Wa.Stylecode) Wc
    On Wb.Warecode = Wc.Warecode

Solution:
go after adjustment optimizer execution plan, the control operation in the WB end, and the distal end MBS7_CRM.WI_WAREBASE table index table fields (STYLECODE) lack of connectivity HINTS index plus the following manner, thus creating an index in the following end of the target optimized optimized COST drops from 7 to 20 more than one hundred, the result may be returned within 2 sec, performance increased a lot.

The distal end of the table to create the index:

create index mbs7_crm.ix_WI_WAREBASE_STYLECODE on mbs7_crm.WI_WAREBASE(STYLECODE)

After tuning SQL:

Select /*+DRIVING_SITE(WB)*/
 Wb.*,
 (Select Wi.Nextarrivedate
    From Mbs7_Oms.Xs_Warearriveinfo@Dc.Moonbasadb.Com Wi
   Where Wi.Warecode = Wb.Warecode) As Nextarrivedate
  From Mbs7_Crm.Wi_Warebase@Dc.Moonbasadb.Com Wb                 ---远端表较大
 Inner Join (Select Wa.Stylecode, Max(Wa.Warecode) As Warecode
               From Mbs7_Crm.Wi_Warebase@Dc.Moonbasadb.Com Wa
              Inner Join (Select Stylecode
                           From Dc_Support.Kh_Visitpage Vis
                          Where Vis.Cuscode = :B1
                            And Vis.Addtime >= Trunc(Sysdate - 31)
                            And Vis.Addtime < Trunc(Sysdate - 30)
                            And Rownum <= 5
                          Order By Addtime Desc) Vis
                 On Wa.Stylecode = Vis.Stylecode
              Group By Wa.Stylecode) Wc
    On Wb.Warecode = Wc.Warecode

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