Some advise on 'WHERE EXISTS' in OWB.

Question

Hello :-) me again.
I have read a number of topics regarding 'WHERE EXISTS' statment and OWB... got confused so i thought i ask your option.
OWB 10 r2.0.1.31 paris/windows
I need to tune one of my maps - nothing fancy, just a simple delete:
I need to delete values from tables A if they are equeals to the values in table B.
Both of my tables have index on matching fields, however it is non unique index and there is no primary or unique key on the tables that i could use. Both tables are not that big either - table A just under 1mil records and table B about 300K records/
So i created simple map -
Mapped table B to table A, set loading type for table A to delete, set 'Match column when deleting' on the matching column .The map was validated without any problems, the tests on a small data set were fine and bob's my uncle!
However, when i submitted the map with 'real' tables - it took a very long time to run (over an hour). I have other more complex maps (and loads of them) and everything is ticking nicely! so what is the problem with this map?
The code generated by OWB for the delete statment as follows:
DELETE FROM TABLE_A
WHERE TABLE_A.MATCH_COL = TABLE_B_MATCH_COL
and it does take ages to run from TOAD.
So i tried running
DELETE FROM TABLE_A a
WHERE exists (select n.MATCH_COL from TABLE_B n
where a.MATCH_COL = n.MATCH_COL)
it took no time at all.
Now how do i have to construct my map in order for OWB to generate WHERE EXISTS code? Is it better to use lookup or set operator? outer join? which one of them would be WHERE EXISTS?
I have another map set up identically but with larger numbers (over 70 mil records in table A). it has been running sinse yesterday lunch time! So any help/thoughts/suggestions on this matter would be greatly appreciated.
Thank you very much
Kind Regards
Vix
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Answer 1

Hi Ed.
Thank you very much for your reply - greately appreciated!
I did look into TOAD when trying to 'tune' it before askling for help. The query does gazzilion tables scans (from Long Ops in TOAD), the main reason why it takes forever is 'db file scattered read' (from waits in TOAD). I checked this job first thing this morning and it's still running!
I have been using OWB Paris for the past year or so and i don't know everything there is not know about it. So i don't know how to make it to produce the code with 'WHERE EXISTS' instead of
DELETE FROM "TABLE A"
WHERE ( "TABLE A.MATCH_COL IS NULL AND :b1 IS NULL
OR "TABLE_A.MATCH_COL" = :b2)
I tried putting non-unique index on MATCH_COL of table A, and put unique index on matching column in table B (ensured that there are no duplicates in table B etc) but oracle pessimiser decided not to use it and i don't really know if the hints are working in OWB and how to make them work with OWB code (i pressume just putting them in the code as normal or is there a 'special' way of doing it?!).
I think i am just going to wrap up my statment in a procedure and just execute the procedure within OWB. I wanted to avoid doing so as i like the auditing granularity with OWB (and if it is a procedure it just calls it, executes it and that's it).
Once again thank you very much for all your help with this issue. May be someone else would have some other ideas how to make it work in OWB? If i manage to improve the performance with this particular map - i will post it here, just in case someone else is having the same problem.
Kind Regards
Vix
Message was edited by:
Vix
- I am takling about my second job that is still running - table A has over 70 mil records and table B has over 600K records.