Re: Mview refresh is much slower in 10g

Hi List,

 

> The last post in that thread (from Pavel Ruzicka) implies that

> the default refresh mechanism did indeed change from 9i->10g,

> but that there is a workaround.

 

Despite the fact that it is not documented change of the default behaviour, I 
thing it is a good feature enabling a 24 hour accessible full refreshable MV.

 

My question - are there experiences in 9i how to workaround the gap on full 
refresh, where the MV is empty (other than simply say there is a loading 
window, don't query the MV)?

 

regards,

 

Jaromir
  ----- Original Message ----- 
  From: Jared Still 
  To: gints.plivna@xxxxxxxxx 
  Cc: davidb158@xxxxxxxxxxx ; oracle-l@xxxxxxxxxxxxx 
  Sent: Thursday, January 18, 2007 9:33 PM
  Subject: Re: Mview refresh is much slower in 10g




  On 1/17/07, Gints Plivna <gints.plivna@xxxxxxxxx> wrote:
    Refresh method has been changed.
    Previously (<9i) for complete refreshes Oracle did truncate mv and
    insert /*+ append */.
    Now (10g) it does delete, normal insert.

    It is discussed for example here
    
http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:15695764787749


  I didn't see in the AskTom article cited where it said that the 
  refresh mechanism changed from truncate/insert append to 
  delete and insert when moving from 9i to 10g.

  It does say that the if the MV is part of a refresh group, a
  complete refresh will be done as delete/insert, rather than
  as truncate/append.

  The last post in that thread (from Pavel Ruzicka) implies that 
  the default refresh mechanism did indeed change from 9i->10g,
  but that there is a workaround.

  I ran a small test to create an MV and do a complete refresh
  on both 9.2.0.6 and 10.2.0.1 that confirms this behavior.

  From the 9i trace:

  PARSING IN CURSOR #15 len=56 dep=1 uid=45 oct=85 lid=45 tim=1141749498683672 
hv=68464594 ad='5cad9640'
  truncate table "JS001292"."MVTEST_MV" purge snapshot log 
  END OF STMT
  ...
  INSERT /*+ APPEND */ INTO 
"JS001292"."MVTEST_MV"("OWNER","TABLE_NAME","TABLESPACE_NAME") SELECT 
"MVTEST"."OWNER","MVTEST"."TABLE_NAME","MVTEST"."TABL 
  ESPACE_NAME" FROM "MVTEST" "MVTEST"
  END OF STMT

  From the 10g trace:

  PARSING IN CURSOR #15 len=35 dep=1 uid=56 oct=7 lid=56 tim=1141749792514219 
hv=540326182 ad='733ed2d0' 
   delete from "JS001292"."MVTEST_MV"
  END OF STMT
  ...
  INSERT /*+ BYPASS_RECURSIVE_CHECK */ INTO 
"JS001292"."MVTEST_MV"("OWNER","TABLE_NAME","TABLESPACE_NAME") SELECT 
"MVTEST"."OWNER","MVTEST"."TABLE_NAME 
  ","MVTEST"."TABLESPACE_NAME" FROM "MVTEST" "MVTEST"


  By changing the refresh method to set atomic_refresh = false, the 
truncate/append
  behavior can be restored. 

  begin
     -- dbms_mview.refresh('MVTEST_MV',method => 'C');
     -- use this with 10g to return to truncate/append behavior
     dbms_mview.refresh('MVTEST_MV',method => 'C', atomic_refresh=>false); 
  end;
  /

  Here's the results of doing so in 10g:

  PARSING IN CURSOR #24 len=57 dep=1 uid=56 oct=85 lid=56 tim=1141750173641027 
hv=455978900 ad='705be890'
   truncate table "JS001292"."MVTEST_MV" purge snapshot log 
  END OF STMT
  ...
  PARSING IN CURSOR #24 len=208 dep=1 uid=56 oct=2 lid=56 tim=1141750173945788 
hv=896677336 ad='6d21e8f0'
  INSERT /*+ BYPASS_RECURSIVE_CHECK APPEND  */ INTO 
"JS001292"."MVTEST_MV"("OWNER","TABLE_NAME","TABLESPACE_NAME") SELECT 
"MVTEST"."OWNER","MVTEST"."TA 
  BLE_NAME","MVTEST"."TABLESPACE_NAME" FROM "MVTEST" "MVTEST"
  END OF STMT

  Nice to know.


  -- 
  Jared Still
  Certifiable Oracle DBA and Part Time Perl Evangelist

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