Thank you so much Mohamed.
*"When generating this execution plan, all things being equal, Oracle will
use the set of hints contained in the SQL Profile or the SQL patch. It is
only when the execution plan has been generated that the SPM finally comes
into play."*
As you mentioned above and aso from the diagram , it's only when the plan
evaluated using either sql patch/stored outline/sqlprofile/hints etc
matches one of the sql_handle with accepted=YES and enabled=YES, then that
plan will be in use. But in case none of the accepted=yes and enabled=yes
sql plan baseline matches with the incoming parsed plan which is
generated using sql patch/hints/sql profile, then that new plan will be
added to the sql plan baseline list with enabled=yes but accepted=NO, and
will be in use. And in this case isn't it incorrect for Oracle to use a
plan which has not been accepted by us in the sql plan baseline? Am I
missing anything here?And if this is true , then there is no guarantee that
the enabled and accepted baselines are always going to be the only plans to
be in use by the sql optimizer.
My thought initially was , if the incoming parsed plan(which has came
through the profile/patch/hints etc..) doesn't match with any of the
baselines( accepted=yes and enabled=yes) baselines then , it should go back
and use one of the baselines( accepted=yes and enabled=yes) having lower
cost only.
On Fri, Dec 17, 2021 at 3:17 PM Mohamed Houri <mohamed.houri@xxxxxxxxx>
wrote:
Hello
*In other words the sql profile or sql patch helps to create new plans
based on the embedded hints however presence of baseline with
accepted +enabled flag as 'YES' is always going to rule at the end. Correct
if my understanding is wrong here?*
The underlined part is incorrect
If you look at the picture I designed in this article
https://hourim.wordpress.com/2015/10/01/oracle-optimizer-and-spm-plan-interaction/
You will realize that the presence of an SPM has *no influence on the
ordinary work of the CBO*. Initially, Oracle will produce its execution
plan ignoring the presence or absence of an SPM.
When generating this execution plan, all things being equal, Oracle will
use the set of hints contained in the SQL Profile or the SQL patch. *It
is only when the execution plan has been generated that the SPM finally
comes into play.*
And what exactly will this SPM do?
It will simply ensure that only the execution plan contained in the SPM
baseline will be used regardless of how this plan has been generated, via
SQL Profile, via SQL patch, or without any of those two features.
Of course, this insurance against a bad surprise(a non-desired execution
plan) is only possible if the plan in the SPM is reproducible at the time
of the execution of the request.
Hope this is clear
Best regards
Mohamed Houri
Le ven. 17 déc. 2021 à 05:18, Pap <oracle.developer35@xxxxxxxxx> a écrit :
Thank you so much Andy.
If I get it correct, it's the sql profile(which is generally a
combination of opt_estimate hints) which oracle will use to evaluate the
plans but it's ultimately the sqlplan baselines (which must be in
accepted+enabled) state which is going to be used finally.
And in scenarios where we use technique to manually create sql profile by
passing exact outline hints (but not with opt_etsimate hints) i.e. using
procedure dbms_sqltune.import_sql_profile where we have ability to pass
the exact full query outline hints which restricts the execution path to
one. In those cases it will mostly fix the exact one execution path for the
query no matter how many times it parses. And in the presence of such a sql
profile , if the sql plan baseline has exactly the same path
enabled+accepted that is going to be used or else it's going to be
completely discarded and the priority will be given to the baseline which
is in accepted+enabled state. (And the discarded plan i.e the parsed plan
using sql profile may be added a new baseline to the list with accepted
flag as NO). Which means sql plan baseline having enabled+accepted flag
as "YES" will take the precedence always irrespective of sql profile/sq
patch etc. Is this understanding correct?
Or
In other words the sql profile or sql patch helps to create new plans
based on the embedded hints however presence of baseline with
accepted +enabled flag as 'YES' is always going to rule at the end. Correct
if my understanding is wrong here?
On Fri, Dec 17, 2021 at 1:53 AM Andy Klock <andy@xxxxxxxxxxxxx> wrote:
Hi Laurentiu,
‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Thursday, December 16th, 2021 at 3:08 PM, Pap <
oracle.developer35@xxxxxxxxx> wrote:
So in cases where the SQL profile or SQL patch has some hints (say FTS
on tab1) which is exactly opposite than that of the one in SQL plan
baseline(say index access for tab1). In that scenario will oracle follow
profile/patch or the baseline path?
If a cursor has "accepted" baselines, then that is typically what the
CBO is going to prefer. When there are multiple accepted plans, then the
CBO will pick the plan with the lowest cost. For cursors that also have a
SQL Profile, then those hints and opt_estimates are applied which may
affect the cost of the baseline plans that the CBO will pick.
Maria wrote a nice article about it [1] in 2012 which I think is still
relevant, but often when you have cursors with lots of baselines, SQL
Profiles, and patches it's time to fix the stats or change the code :)
Andy K
[1]
https://blogs.oracle.com/optimizer/post/what-is-the-difference-between-sql-profiles-and-sql-plan-baselines
--
Houri Mohamed
Oracle DBA-Developer-Performance & Tuning
Visit My - Blog <http://www.hourim.wordpress.com/>
Let's Connect -
<http://fr.linkedin.com/pub/mohamed-houri/11/329/857/>*Linkedin
Profile <http://fr.linkedin.com/pub/mohamed-houri/11/329/857/>*
My Twitter <https://twitter.com/MohamedHouri> - MohamedHouri
<https://twitter.com/MohamedHouri>
