Re: Things to consider during upgrade/migration

Hi Lok,

I suspect the answer to this probably lies in your corporate appetite for risk and the reasons for the upgrade. The original question was "How do I upgrade or migrate with minimal changes to performance?". Andy has covered this (I might have added set OFE to the source version as well). The approach of capturing baselines for the application workload and using them is great for predictable performance and is *really* useful as Andy says for finding SQL statements that might need attention. This enables you to minimize the amount of performance work done at upgrade time.

However, if you are moving from 11.2 to 19c (~ten years of development), and especially if you are moving platform as well you may well want *not* to maintain performance as it was, but to take advantage of the various enhancements that come with later versions of the database, to do that you will need to allow the database to use the CBO as intended by Oracle and then fix regressions on a case by case basis. You'd likely end up with a better performing application, but with a higher risk and a greater testing requirement. Given the amount of change that you are intending to undertake, I suspect that this would actually be a better approach.

On Sun, Nov 14, 2021 at 5:16 PM Lok P <loknath.73_at_gmail.com> wrote:

> Thank you so much Andy, Clay and Mladen.
>
> If I got it right, with respect to gathering system statistics in Exadata
> mode, we should not do it unless justified/tested. And table and
> dictionary stats should be treated in the same way as it is there in older
> version 11.2.0.4.
>
> With regards to capturing sql plan baselines for all sqls. I have some
> doubts. We already have optimizer_use_sql_plan_baselines set as TRUE in our
> database. So, are you suggesting to alter the
> optimizer_capture_sql_plan_baselines to TRUE , 2-3days prior upgrade which
> will ensure our full application workload runs at least 2-3 times before
> upgrade so that all the baseline will be captured without missing any sql.
> And then at the same time we will turn optimizer_use_sql_plan_baselines as
> False, so that those will not be used automatically by the queries until we
> manually evolve and accept it. And post upgrade if any sql misbehaves we
> will scan the captured baselines and set that enabled for that sql only. Is
> this what you are suggesting?
>
> Btw in the above approach, I see some issues as , we currently
> have optimizer_use_sql_plan_baselines set as TRUE which is default. And we
> are already having some baselines and sql profiles for few of the critical
> sqls , so we can not turn that off for doing a bulk sql baseline capture
> for upgrade. So is there any workaround for this? In our case if we just
> want to capture the baselines but we want to keep control of evolving and
> applying the plan with us i.e manually but not by oracle automatically,
> how to do that? Is it possible without setting the
> optimizer_use_sql_plan_baseline false? As I tested, it attaches the
> baseline to the SQL by default and that way we will have all our SQL
> queries have the baseline attached at the end of the capture process. We
> normally avoid SQL profile, baselines, hints and only want to go for it in
> real need. And after upgrading we just want to attach a baseline if any SQL
> behaves badly and we have to go for a quick fix and we will do that
> manually. Can you please guide me here?
>
>
>
> On Sun, Nov 14, 2021 at 3:06 AM Clay Jackson (cjackson) <
> Clay.Jackson_at_quest.com> wrote:
>
>> What Mladen and Andy said – I would pay very serious attention to their
>> wisdom; born of many years 😊. ESPECIALLY the parts about
>>
>> 1. How different 19 is from 11 and the Exadata is from the HP
>> 2. Collecting baselines for ALL SQL – the time you spend up from will
>> save more than that troubleshooting on the “back end”
>> 3. TEST EVERYTHING
>>
>>
>>
>> In my position, I talk to customers/prospects going through similar
>> upgrades/migrations and those who follow(ed) Steps 2 and 3 (and understood
>> the differences) had SIGNIFICANTLY better success than those who tried to
>> “shortcut” the process.
>>
>>
>>
>> Clay Jackson
>>
>>
>>
>>
>>
>> *From:* oracle-l-bounce_at_freelists.org <oracle-l-bounce_at_freelists.org> *On
>> Behalf Of *Lok P
>> *Sent:* Saturday, November 13, 2021 10:47 AM
>> *To:* Oracle L <oracle-l_at_freelists.org>
>> *Subject:* Things to consider during upgrade/migration
>>
>>
>>
>> *CAUTION:* This email originated from outside of the organization. Do
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>>
>>
>>
>> Hello Listers, With respect to having a safe upgrade(say from 11.2 to
>> 19C) or migration(From HP to Exadata) experience with minimal performance
>> issues. Is there any guideline we should follow like setting up exadata
>> system stats in case the target database is going to be exadata, Or
>> verifying dictionary stats/table stats etc in a certain way. Want to know
>> experts' views, if there are any such guidelines?
>>
>> Regards
>>
>> Lok
>>
>

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Niall Litchfield
Oracle DBA
http://www.orawin.info

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