Re: cardinality feedback in 19c

Hi Mohamed,

"_optimizer_use_feedback" works differently since 12.2 (and on 12.1.0.2 after the patch for bug# 22652097):
https://antognini.ch/2016/10/adaptive-query-optimization-configuration-parameters-preferences-and-fix-controls/ So it works pretty good now and with the disabled OPTIMIZER_ADAPTIVE_STATISTICS by default, I do not change _optimizer_use_feedback now.
If I need to fix some rare issues, I do that only for specific queries using SQL profiles or patches.

On Tue, Apr 27, 2021 at 1:29 PM Mohamed Houri <mohamed.houri_at_gmail.com> wrote:

> Hello
>
> In 11g and 12c, I used to disable the parameter _optimizer_use_feedback
> because the re-optimization was always producing a suboptimal execution
> plan. But I kept this parameter enabled while upgrading to 19c. And, after
> more than 10 19c upgrades I haven’t noticed any performance issue induced
> by the cardinality feedback feature. Until today, where a bunch of queries
> changed their execution plan (from 1 second on average to 300 seconds)
> because of cardinality feedback usage
>
> Are you still disabling this feature in 19c?
>
> Thanks
>
> Mohamed Houri
>
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> Houri Mohamed
>
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-- 
Best regards,
Sayan Malakshinov
Oracle performance tuning engineer
Oracle ACE Associate
http://orasql.org

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