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05144 - Record deletion and index performance?

05144 - Record deletion and index performance?

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Record deletion and index performance?

I'm going to state this as clearly as I can, but I don't understand it
completely myself:

We've got an archive consultant in who initially raised the question. His
concern is what happens when many records of a table are deleted? In the past
(in, ...ahem... a non-AS/400 shop), he's witnessed a problem where many records
get deleted, which fragments the corresponding index. Apparently, with a
"fragmented index", the optimizer eventually starts processing sequentially.
Never heard of such a thing on the AS/400, but I've never deleted half of a
100GB table before, either! (Working on COEP, by the way, in a 4.6C
environment.)

Related question: assuming that we delete half of a 100GB table and try to
organize it. I see three choices:

1 - OS/400 reorganizes it in place--pretty dangerous, probably not done
2 - OS/400 copies everything out, and copies only the good stuff back--seems
inefficient
3 - OS/400 copies just the good stuff out, then renames tables

If I had to guess, I would think it follows #3. My question comes down to this:
if I'm reorganizing a 100GB table that's got half of the records deleted, what
do I need for free space in order to reorganize--100GB or 50GB?

Thanks for any replies!

Jim Doll, Perrigo SAP Technical Support


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