RE: Things to consider during upgrade/migration

From: Mark W. Farnham <mwf_at_rsiz.com>
Date: Wed, 17 Nov 2021 12:47:31 -0500
Message-ID: <561401d7dbdb$324d0c70$96e72550$_at_rsiz.com>

There are many ways. I would suggest the simplest for headcount 9 is to:  

1. Create a custom table as select * from “the baseline plan table” with your current nine plans.
2. Hint the 9.
3. change the default to false
4. start capturing everything.
5. run long enough to get everything you care about
6. copy all the baselines somewhere custom for reference, because doing an upgrade in place you won’t be able to recreate them after the upgrade.
7. stop capturing everything
8. drop all the baseline plans
9. copy the custom table from step 1 back into the baseline plan table. It’s small, so probably leave it around “forever” as a reminder.
10. change the default back to the default of true

I am old and rusty, so chime in if one of these steps won’t work out of the box.  

Consider trying each of those 9 sqls without the baseline, one at a time, because discarding obsolete custom tuning of all sorts when the default behavior of Oracle becomes at least as good reduces the detritus of age.  

The goal of the optimizer is good plans (with as little done by the customers as possible). Your goal is to just get better with no backsliding on the performance your users care about.  

May your upgrade be BORING.  

mwf      

From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Lok P Sent: Wednesday, November 17, 2021 12:28 PM To: Mark W. Farnham
Cc: Andy Sayer; Clay Jackson (cjackson); Oracle L Subject: Re: Things to consider during upgrade/migration  

Yes Mark, so my point was, we already have ~9 sqls which are using baseline in current 11.2. version and of course have optimizer_use_sql_plan_baselines set as TRUE(which is default). But Now that we will be setting optimizer_capture_sql_plan_baselines to TRUE a few days before 19C upgrade on production to get hold of all the possible sql and their plans(say we captured ~1000 sqls baseline), but we don't want all of those to be enabled at that same moment. rather we want only to enable the baseline for those ~9 old sqls + additional few sql (say e.g. 3 sqls ) which misbehaved/changed plan post upgrade to 19c. And we want to drop/get rid of those other ~997 sql baselines from our 19C version database (which we captured initially just for our safety). So considering its inplace upgrade and we don't have an exact test environment like RAT, is there a way to achieve this in the existing production database? I am still unable to get it clearly.  

On Wed, Nov 17, 2021 at 10:29 PM Mark W. Farnham <mwf_at_rsiz.com> wrote:

I thought the point was he has enabled the use of all the baselines he currently has en masse by a default parameter, so he wants to be able to get back to just those being stored.  

Did I misread something?  

From: Andy Sayer [mailto:andysayer_at_gmail.com] Sent: Monday, November 15, 2021 5:29 PM
To: mwf_at_rsiz.com
Cc: Clay Jackson (cjackson); Oracle L; loknath.73_at_gmail.com Subject: Re: Things to consider during upgrade/migration  

“ As i had posted earlier, I am still wondering how to isolately enable the sql plan baselines to only specific sqls manually rather than forcing it to be enabled for all the captured baselines? ”

Capture ALL baselines (either with the parameter or just loop through your application sql_ids and the dbms_spm function). Keep using baselines with your existing parameter. You can turn off the capture just before you upgrade if you really wanted (I leave it permanently true).  

No need to do anything special with your existing baselines, just keep them as they are (nothing will happen to them unless you manually disable them).  

Thanks,

Andy  

On Mon, 15 Nov 2021 at 21:45, Mark W. Farnham <mwf_at_rsiz.com> wrote:

Or just export the current contents and use your favorite method to restore it as the contents later…  

From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Lok P

Sent: Monday, November 15, 2021 2:53 PM
To: Mark W. Farnham
Cc: Clay Jackson (cjackson); Oracle L
Subject: Re: Things to consider during upgrade/migration  

As i had posted earlier, I am still wondering how to isolately enable the sql plan baselines to only specific sqls manually rather than forcing it to be enabled for all the captured baselines?

Note- We have currently optimizer_use_sql_plan_baseline set as default true which is helping few of the existing sqls already. So we can not turn it false. And keeping it True is again going to make all the captured baselines to be enabled, so how should we deal with this?  

On Mon, Nov 15, 2021 at 7:22 PM Mark W. Farnham <mwf_at_rsiz.com> wrote:

AND, (not but at all),  

Don’t be hesitant to discard a few false starts. Make sure your timeline includes time for a few fresh starts.  

IF you have a way to simulate the activity including transactions, standard reports, and most common ad hoc reports for a five month period of December, January, February, March, and April for a January 1st year end, that will cover a year end and a quarter end, which tend to be the most important. IF special things happen at year and quarter ends and you don’t do this, you are in extreme violation of #3 below.  

IF you have time period comparison reports for, say, last year compared to this year and the time to shove all data conflicts with the desire for multiple trial conversions and dress rehearsals make sure you get enough months to make the comparison reports realistic.  

IF you have a lot of moribund data (data that is no longer allowed to be changed) consider physically re-ordering, partitioning, and making such data isolated in read only spaces as part of the migration. As needed for retrograde plan or iso-plan performance outliers, extra specific indexes (and/or best cluster factor and attribute ordering to match queries of existing indexes) may be extremely useful to improve performance. The extra time to convert is often time well spent in both size and speed.  

IF you can simulate as suggested, that may tempt you to go light on suggestion #2 below, ignoring the things that seem fine and just snapping the baselines that have problems in your “test migration” when everything on the destination is fresh and new. Don’t skip suggestion #2 unless you plan to have the old machine available for years. Transactions can change the texture of the data over time such that plan changes erupt differently in the new environment as time passes. IF the old machine is gone, all those baselines are your time machine to keep life BORING. BORING is good in IT operations. The excitement should be innovative use of well running technology, not firefighting to keep the technology from burning up.  

Good luck. JL also has a blog thread of things that can go bump in the night when you “didn’t change anything” that is a useful read to help THINKING CLEARLY about things that erupt during your several dress rehearsals.  

And remember: Two complete dress rehearsals with NO CHANGES before you pull the trigger on the real migration. (Farnham’s Law of Sane Migrations, often violated at great pain).  

From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Clay Jackson ("Clay.Jackson") Sent: Saturday, November 13, 2021 4:36 PM To: loknath.73_at_gmail.com; Oracle L
Subject: RE: Things to consider during upgrade/migration  

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 not follow guidance, click links, or open attachments unless you recognize the sender and know the content is safe.  

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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Received on Wed Nov 17 2021 - 18:47:31 CET