Re: 12.1 Optimizer feature stability

You could view 12.1 as a special case.

The adaptive optimisation features caused so many stability problems to so many sites that official advice came out suggesting people adjust a couple of hidden parameters to disable some of the adaptability features. If you're going to have to start setting those hidden parameters anyway you might as well just set OFE - provided you remember that it doesn't guarantee that EVERY optimizer change will be reversed (and, in particular) some of the optimizer bugs fixed in 12.1 may not be unfixed by setting the OFE backwards.

Regards
Jonathan Lewis

On Mon, 11 Jan 2021 at 13:17, Pap <oracle.developer35_at_gmail.com> wrote:

> Thank you Shane.
>
> Actually team says 12.1 is the buggier one and also all the .1 releases
> having most of the issues , so trying to play safe by keeping OFE at 11.2.
> So I wanted to check if it's really true. But i think , as per your point,
> we should really stick with all defaults for that version, i.e. in our case
> OFE- 12.1 only.
>
> Thanks and regards
> Pap
>
> On Mon, Jan 11, 2021 at 4:59 PM Shane Borden <sborden76_at_yahoo.com> wrote:
>
>> One last thing, it’s not like Oracle really tests this configuration
>> either. So if you really need OFE or some else set for a query, do it
>> with a profile or hint for that sql not systemwide.
>>
>> Shane Borden
>> sborden76_at_yahoo.com
>> Sent from my iPhone
>>
>> > On Jan 11, 2021, at 6:18 AM, Shane Borden <sborden76_at_yahoo.com> wrote:
>> >
>> > On an upgrade, I always reset the parameters to all defaults unless
>> you know you need to address a specific requirement such as Peoplesoft or
>> EBS.
>> >
>> > Doing it this way gives you a chance to get back to default
>> characteristics and eliminate technical debt that people likely can’t prove
>> the need to be there anyway.
>> >
>> > Also, don’t let the App team dictate how to set it up unless they can
>> prove the need. The worst reason ever is “that’s the way it’s always
>> been”.
>> >
>> > Shane Borden
>> > sborden76_at_yahoo.com
>> > Sent from my iPhone
>> >
>> >> On Jan 11, 2021, at 4:57 AM, Pap <oracle.developer35_at_gmail.com> wrote:
>> >>
>> >> 
>> >> Hello All, We are moving from version 11.2.0.4 to version12.1.0.2.0 of
>> Oracle. We can't go to the latest versions(like 19C/18C) because of certain
>> application dependencies which are running on this database. Team is
>> suggesting to keep the optimizer_feature_enable as it was for existing
>> version i.e. 11.2.0.4, as because there are issues/bugs for version
>> 12.1.0.2.0.
>> >>
>> >> So I wanted to check with experts here , if it's really so and have
>> such a bad experience with OFE- 12.1.0.2.0 and we must keep the optimizer
>> feature at 11.2.0.4 even if the database version would be 12.1.0.2?
>> >>
>> >> For information, We do use a lot of Global temporary tables in our
>> application code, but then we are thinking these will get the benefit of
>> the private session level stats on OFE- 12.1 and it won't happen such if we
>> keep the OFE at 11.2. Even if we don't change the code to gather stats on
>> the GTT immediately during migration , then that will still keep on using
>> dynamic sampling(in absence of session level stats) as it used to happen on
>> version 11.2. And gradually we will change our code to gather session level
>> stats in application code where estimation is going bad impacting execution
>> path.
>> >>
>> >> Regards
>> >> Pap
>> >>
>>
>>

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