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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