Re: Sudden plan change related to "VIEW PUSHED PREDICATE" with cost difference of 1M VS 13G

Dont have DML rights on prod so explain plan is not working for me for this MERGE but i fetched it from admin guys. Below is the plan with OFE ('12.1.0.2') and removing ordered hint. And i am seeing same plan even by just removing ordered hint.

Also something interesting, when i ran it as a SELECT statement, its going for thr JPPD , so it seems , its the MERGE query which is facing some blocking transformation. And i am seeing hint added as /*+ NO_MERGE */ in the unparsed query in the 10053 trace, not sure if its expected or point towards any oddity?

And another interesting thing , when i had tried by pushing the hint which Andy suggested i.e to make the plan as HASH JOIN + FULL SCAN , but the resulted plan was totally different though. It was nested loop + indexed access. But the sql is getting finished with that path. So we can definitely push this as a profile. And this plan is having cost ~1M i.e. lot less than the path its currently opting for by default. Still unknown about the exact root cause/bug fix which is causing though. But we have atleast got a workaround. Thank you so much.

Posted the above plans in below link.

https://gist.github.com/oracle9999/b3ff18f62f2ba6d0c0ffe448895e1046

On Fri, 13 May 2022, 4:35 pm Noveljic Nenad, <nenad.noveljic_at_vontobel.com> wrote:

> Have you considered following action plan?
>
> “
>
> - Generate the plan without optimizer_features_enabled (according to
> the outline it is set to 11.2.0.4)
> - Remove the ORDERED hint and check if it has any impact
> - Duplicate the database and upgrade it to 19c just to see if the
> problem reproduces in a newer release
>
> “
>
> The first two points are trivial and don’t require much effort.
>
>
>
> *From:* Pap <oracle.developer35_at_gmail.com>
> *Sent:* Freitag, 13. Mai 2022 07:21
> *To:* Noveljic Nenad <nenad.noveljic_at_vontobel.com>
> *Cc:* Oracle L <oracle-l_at_freelists.org>; Andy Sayer <andysayer_at_gmail.com>;
> Mohamed Houri <mohamed.houri_at_gmail.com>
> *Subject:* Re: Sudden plan change related to "VIEW PUSHED PREDICATE" with
> cost difference of 1M VS 13G
>
>
>
> **** E-Mail from outside Vontobel:* Do not click on links or open
> attachments unless you know the content is safe. ***
>
> * _at_Nenad *
>
> *"Are there any lines between the two lines mentioned above (“updated best
> state” and “Will not use JPPD” that might give the reason for not using
> JPPD? "*
>
> There are no lines between these two in the trace file.
>
>
>
> On Fri, May 13, 2022 at 1:45 AM Noveljic Nenad <
> nenad.noveljic_at_vontobel.com> wrote:
>
> Hello Pap
>
>
>
> I revisited my suggestion about column statistics - it was wrong. The low
> selectivity led to the JPPD transformation cost similar to the one that was
> in the plan with JPPD.
>
> JPPD: Updated best state, Cost = 39.073380
>
>
>
> If we multiply the cost above with the number of rows of the outer query
> block and add the cost of the outer join query block, we get the total cost
> of the plan with JPPD. It’s much lower than the plan without JPPD and
> similar to the cost of the good plan you’ve had previously:
>
> 20710 * 39.073380 + ~260K ~ 1M
>
>
>
> So JPPD should definitely be selected.
>
>
>
> The optimizer figured out that correctly and updated the best state with
> the cost of JPPD (39.07 is the cost of a single iteration):
>
>
>
> JPPD: Updated best state, Cost = 39.073380
>
>
>
> But then, it discarded it soon, for still unknown reason:
>
>
>
> JPPD: Will not use JPPD from query block SEL$B29E968D
>
>
>
> You mentioned that you edited out some lines from the optimizer trace. Are
> there any lines between the two lines mentioned above (“updated best state”
> and “Will not use JPPD” that might give the reason for not using JPPD? As
> already mentioned, the cost isn’t the reason.
>
>
>
> If not, the following might be the reason:
>
> A Optimizer applied some heuristics without logging it or
>
> B The correct decision got overridden due to a bug
>
>
>
> Could you try following:
>
> - Generate the plan without optimizer_features_enabled (according to
> the outline it is set to 11.2.0.4)
> - Remove the ORDERED hint and check if it has any impact
> - Duplicate the database and upgrade it to 19c just to see if the
> problem reproduces in a newer release
>
>
>
> Best regards,
>
>
>
> Nenad
>
>
>
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