RE: Mview refresh is much slower in 10g

We set up 2 identical materialized views - *_MVW_1 and *_MVW_2
 
Refresh them on an alternating schedule.  As part of the refresh jobs,
recreate a synonym pointing to the newly refreshed view as the last step
and use that synonym to reference the materialized view.


Steve Smith

Envision Technology Partners / MSHA MSIS Team

Desk: 303-231-5499

 

 

-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of jaromir nemec
Sent: Thursday, January 18, 2007 3:03 PM
To: jkstill@xxxxxxxxx; gints.plivna@xxxxxxxxx
Cc: davidb158@xxxxxxxxxxx; oracle-l@xxxxxxxxxxxxx
Subject: 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 <mailto:jkstill@xxxxxxxxx>  
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:1569
5764787749



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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