Re: Slow Update

I didn't say "swap the stats" I said "swap some details of the stats". It's a fine distinction, but I certainly wouldn't expect Amit to ask for and import a full metadata export with stats of Jo's table.

Don't forget that the plan is set by the optimizer's best guess of what's going to happen at run time, so it's fairly irrelevant that one of the components of the guesswork didn't execute at all. However, it feels a little suprising that adaptive execution didn't come into play to switch the hash join to a nested loop join (it is 19c, after all) when the vw_nso_1 completed and acquired so little data. (I can't see any place in the output where we could find out if adaptive execution had been disabled - I thought it would show in the optimizer environment, but there's no mention there. Maybe there's a restriction on adaptive execution when there are "conditional" subqueries in play.)

Regards
Jonathan Lewis

On Fri, 3 Nov 2023 at 11:13, Timur Akhmadeev <timur.akhmadeev_at_gmail.com> wrote:

> I think swapping stats is not a good idea since the data is different -
> things like ORG_ID at least - which will impact estimates with different
> inputs in different DB. Changing num_distinct/num_rows/similar things might
> be OK.
> It's best to gather stats on the table and indexes and see if the plan
> changes - perhaps the index/table stats are not in sync and causing this
> bug.
> Also I find it funny that lines 15-17 are not even executed because of the
> conditional FILTER operation, yet causing misestimates and wrong choice of
> the join method.
>
>
> On Fri, Nov 3, 2023 at 1:02 PM Jonathan Lewis <jlewisoracle_at_gmail.com>
> wrote:
>
>> There are times when I get to feel really smug!
>>
>> Maybe you could swap some details of the stats on that table, its indexes
>> and the column in the critical predicates with Amit to help identify why
>> the silly cardinality estimate has appeared.
>>
>> Regards (and thanks)
>> Jonathan Lewis
>>
>> On Fri, 3 Nov 2023 at 08:23, Holvoet Jo <J.Holvoet_at_dwl.be> wrote:
>>
>>> I can find that exact same sql_id in our Oracle EBS db as well, and our
>>> execution plan is basically doing what Jonathan says : a NL join between
>>> VW_NSO_1 and a unique index scan on PO_LINE_LOCATIONS_U1 instead of your
>>> hash join with a full table scan. We end up with a cost of 6 for the update
>>> and execution times in the centisecond range (although here it is hardly
>>> ever executed – at most once every few days).
>>>
>>>
>>>
>>> Regards
>>>
>>> Jo
>>>
>>>
>>>
>>>
>>>
>
> --
> Regards
> Timur Akhmadeev
>

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