Using ALL_WMD_MODIFIED_TABLES,_DIFF view & SetDiffVersions

Question

Hi All,
I need suggestions on the below usage of ALL_WMD_MODIFIED_TABLES,_DIFF view & SetDiffVersions procedure in OWM.
Requirement: Need to determine modified rows between two savepoints in a workspace and update modified rows.
Data:
Workspace name -'WPS1'.
Savepoint1 name -'WPS1_SVP1'.
Savepoint2 name -'LATEST'.
What I am doing?
1.Goto Workspace.
EXEC Dbms_wm.Goto_Workspace('WPS1');
2. Run below query on 'ALL_WM_MODIFIED_TABLES ' to identify modified tables and keep them in a collection say 'Modified_Tables'.
select distinct TABLE_NAME From ALL_WM_MODIFIED_TABLES where WORKSPACE='&WPS';
3.Set DiffVersions procedure between two Savepoints.
EXEC Dbms_wm.SetDiffVersions('WPS1','WPS1_SVP1','WPS1','LATEST');
4. Loop through the 'Modified_Tables' collection and run the below query on {table_name}_DIFF Views.
+select * from {table_name}_DIFF where WM_DIFFVER = 'WPS1,LATEST' and WM_CODE in ('I', 'U','NE');+
5. Update rows on modified tables.
Inputs needed:
Please provide suggestions/recommendations/feedback/limitations/best practises of the above used OWM elements (ALL_WMD_MODIFIED_TABLES,_DIFF view & SetDiffVersions.
Also provide me feedback on improving performance of any of the above queries.
My frontend application is based on .NET and it is running very slow.
Thanks in advance.

Answer 1

Thanks Ben in responding to this problem!
I am using OWM 10.2.0.5.0
The gather statistics on WMSYS schema did not help either. Following is the performance statistics that I observe
•     _DIFF view selection (select *) for following number of row change
o     for 50K row change - 11 minutes
o     for 30K row change - 6.5 minutes
o     for 20K row change - 5 minutes
o     for 10K row change - 2.4 minutes
•     _DIFF view selection (select (1)) for following number of row change
o     for 50K row change - 12 minutes
o     for 30K row change - 6.8 minutes
o     for 20K row change - 4.8 minutes
o     for 10K row change - 2.4 minutes
While waiting for the OTN response, I created an SR. Following is what Oracle says.. They are asking not to gather statistics ! I tried the rule based optimizer suggested by Oracle. It did not help. I have responded back to Oracle with my observation.
I think you have run into following bug -
Bug 7581604: BAD PERFORMANCE OF QUERY AGAINST _DIFF IF VERSION ENABLED TABLE IS ANALYZED
This bug is fixed in11.2.0.1. There is no fix for this bug in 10.2. But you can use one of the following workarounds -
1. Using a RULE hint in the query to force use of the Rule Based Optimizer, for example:
select /*+ RULE */ * from <Table>_DIFF
2. dont gather statistics !!!! when stats are gathered for a version enabled table, querying _DIFF view starts using a full table scan execution plan instead of index range scan.
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