Hello
*But surprisingly, i am seeing it's still keep creating new baselines. Why
is it so?*
If you reread the CBO interaction diagram in the presence of an SPM, you
will realize that, whatever the situation is, in presence of an SPM, the *CBO
plan* is
1) either equivalent to the plan already in the SPM baseline and not
inserted again into the SPM baseline (completely on the left in the
diagram)
2) or inserted into the SPM baseline when it is not equivalent to the SPM
baseline (completely on the right in the diagram)
https://hourim.wordpress.com/2015/10/01/oracle-optimizer-and-spm-plan-interaction/
*And does that mean, we need to delete the baselines fully if we don't want
to use them for a specific SQL?*
No; you need to prevent Oracle from automatically evolving the CBO plans
inserted in the SPM Baseline by changing the following parameter value from
TRUE to FALSE
SELECT
parameter_name,
parameter_value
FROM
dba_advisor_parameters
WHERE
task_name = 'SYS_AUTO_SPM_EVOLVE_TASK'
AND parameter_name in ('ACCEPT_PLANS','ALTERNATE_PLAN_BASELINE')
;
PARAMETER_NAME PARAMETER_VALUE
------------------------------ ----------------
ALTERNATE_PLAN_BASELINE EXISTING
ACCEPT_PLANS TRUE
BEGIN
DBMS_SPM.SET_EVOLVE_TASK_PARAMETER(
task_name => 'SYS_AUTO_SPM_EVOLVE_TASK' ,
parameter => 'ACCEPT_PLANS',
value => 'FALSE');
END;
/
PARAMETER_NAME PARAMETER_VALUE
------------------------------ ----------------
ALTERNATE_PLAN_BASELINE EXISTING
ACCEPT_PLANS FALSE
Best regards
Mohamed Houri
Le jeu. 8 sept. 2022 à 10:02, yudhi s <learnerdatabase99@xxxxxxxxx> a
écrit :
We did turn off the auto capture and also disabled the baselines those
were created through auto capture process. But surprisingly, i am seeing
it's still keep creating new baselines. Why is it so?
Does it mean, it doesn't check the enabled flag but just see if any
baseline exists in past for that SQL in dba_sql_plan_baselines, if yes,
then keep creating or evaluating new one for those sqls? And does that
mean, we need to delete the baselines fully if we don't want to use them
for a specific SQL?
On Thu, 8 Sep 2022, 11:15 am Lok P, <loknath.73@xxxxxxxxx> wrote:
If you want to selectively use the baseline but not all those captured
then I think after turning OFF the auto capture process you can disable all
of those 300k baselines those are created as part of your 11g auto capture
process leaving the ones those are really in use in 11g. Then when you move
to 19c just use or enable the ones which are regressing or showing sub
optimal performance only on 19c.
On Mon, 5 Sep 2022, 6:24 pm yudhi s, <learnerdatabase99@xxxxxxxxx> wrote:
Thank you Mohamed.
I checked current production environment(still on 12.1) , so far we have
the capture process turned on for ~7days and it has ~373K baselines created
for ~299K distinct sql_handles or sqls. I didn't see the spike in
concurrency waits in overall database level though. Even if i see the
number of baselines created for few of the sql_handles is 20+ , but all of
those having only one baselines with accepted=YES and enabled=YES other
were created with accepted=NO. Out of all the ~377K baselines , I see only
two sqls/sql_handles having two baselines each with both enabled='YES' and
accepted='YES'.
So as per below algo, in most of our cases optimizer will only go
through "one" evaluation of the accepted+enabled plan and thus may not
cause a parsing storm. And if we ensure to keep one 'accepted=yes' baseline
for any sql that should be okay to not cause concurrency issue during
parsing. Also as Pap mentioned , i hope during parsing issue for any SQL,
dropping the baselines and creating as sql profile out of those plan may be
the way to go. Correct me if my understanding is wrong.
https://hourim.wordpress.com/2015/10/01/oracle-optimizer-and-spm-plan-interaction/
Also in below doc page-5 , its mentioned in the auto capture process
"Regardless of which method you use to initially create a SQL plan
baseline, any subsequent new plan found for that SQL statement will be added
to the plan baseline as an unaccepted plan. This behavior is not dependent
on the initialization parameter OPTIMIZER_CAPTURE_SQL_PLAN_ BASELINES and
will occur even if this parameter is set to FALSE (the default)."
https://www.oracle.com/technetwork/database/bi-datawarehousing/twp-sql-plan-mgmt-19c-5324207.pdf
On Mon, 5 Sep 2022, 12:55 pm Mohamed Houri, <mohamed.houri@xxxxxxxxx>
wrote:
Hello,
Your 12c SPM execution plans will be used only if they are reproducible
in 19c. Otherwise, Oracle will use the 19c plan it produces at hard parse
time.
So, in 19c, you will be in one of the two following situations:
1. CBO comes up with a new 19c plan present in the SPM baseline
a) You will use the 19c CBO (or the 12c SPM plan)
2. CBO comes up with a new 19c plan not present in the SPM
baseline
b) Your 12c SPM baseline plans are reproducible: you will use the
SPM plan
c) Your 12c SPM baseline plans are not reproducible and you will
use the 19c plan
*How should we be able to make use of 19C features or plans on top
of the existing baselines post migration? *
If you are in situation n°1 it means that your queries are processed by
Oracle in the same way in both releases 12c and 19c
However, if you are in situation n°2 b), then it is possible that the
new 19c plan is better (or worse). And this is where you need to
strategize. Opt for stability and keep using the SPM 12c plans (you will
have to prevent Oracle from evolving the 19c plan by accepting it as a new
valid plan in the baseline), or let Oracle automatically evolves the 19c
plan
But I think that you have opted for a bad strategy which consists in
capturing execution plans of all queries executed twice. This will fill the
SYSAUX tablespace and introduce considerable parsing effects, especially
for queries that change plans too often (due to ACS for example). If
the new 19c plan is not present in the SPM baseline and this SPM baseline
contains more than 2 ACCEPTED AND ENABLED plans, then all those
execution plans will enter in competition to determine the best one. And
you can imagine that this is not free in terms of CPU and Cursor Pin S wait
on X and library cache lock wait events.
Best regards
Mohamed Houri
Le sam. 3 sept. 2022 à 20:10, yudhi s <learnerdatabase99@xxxxxxxxx> a
écrit :
Thank You Jonathan.
Actually we were not having an environment which is close to
production in terms of data volume and data pattern and infrastructure.
And
currently we have turned on the "capture baseline" flag to TRUE in
production itself which is on 12.1 version and we already have hundreds of
thousands of sql baselines getting captured in production on a daily
basis.And i noticed the "use baseline" flag is already set as default
TRUE.
And we are planning to set the capture baseline flash now to FALSE as we
have all types of workloads covered till now. In this situation, how
should
we be able to make use of 19C features or plans on top of the existing
baselines post migration?
On Sat, Sep 3, 2022 at 8:49 PM Jonathan Lewis <jlewisoracle@xxxxxxxxx>
wrote:
One fairly standard approach is to test on a full-size backup copy of
production with no SQL baselines to find the statements that show much
worse performance in 19c, then go back to the 11g versions and capture
plans for only those statements before the live upgrade.
Regards
Jonathan Lewis
On Sat, 3 Sept 2022 at 14:21, yudhi s <learnerdatabase99@xxxxxxxxx>
wrote:
Thank you All.
I understand for some of the specific scenarios like fixing wrong
results related to bugs from some transformation etc, it may happen
that a
certain plan is not reproducible exactly on 19c which was there in 11.2
/12.1 versions. In these cases in the19c version, it will come up with a
new plan which will eventually not match with any of the accepted old
baselines and thus the optimizer will forcibly choose a different path
altogether and create that as a new accepted baseline.
However, doesn't it sound odd that in cases where, of all those
hundreds of thousands of sqls using one of the captured baselines from
12.1
by auto capture process which are now in an accepted state from the 12.1
version, has to be manually evolved and accepted to use the 19C feature
or
new plans? Considering enabling auto evolve jobs as riskier to go for.
So I
wanted to understand what is the standard or lesser riskier suggested
way
of doing this when moving to the 19c version?
--
Houri Mohamed
Oracle DBA-Developer-Performance & Tuning
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