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

• _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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