Thank You So much. This database is on version 19.9 , but OFE is still
11.2.0.4.
So it means at least the optimizer mode as 'first_row_1' has not to be set
as global but rather should be done only in specific cases on session level
if required. And thus, this non default value is not a guidance from
peoplesoft product.
However, not able to get it fully , when you said *"** of course, you
should delete these altered sessions wherever you find them." . *Do you
mean to say , we need to set it back to "all_rows" after the intended
query/session finishes with "first_rows_1" optimization mode? Please
correct me if I'm wrong.
On Tue, Jan 18, 2022 at 1:35 PM Mohamed Houri <mohamed.houri@xxxxxxxxx>
wrote:
Pap
Regarding PeopleSoft and its recommendations concerning certain parameters
of the CBO, we've talked about it a lot here on this list, so I'd
definitely like to clarify that from my experience with at least 3
different applications using PeopleSoft.
Firstly, the optimizer_mode= first_rows_1 parameter is not set at a
global level but only via a couple of altered sessions. And yes, of course,
you should delete these altered sessions wherever you find them. This is
exactly what I did for my 3 clients.
Second, setting the _optimizer_skip_scan_enabled parameter to FALSE is
indeed suggested by PeopleSoft. I set it to TRUE globally in the first days
of testing in UAT. And you should do the same.
Finally, PeopleSoft suggests changing the _unnest_subquery parameter to
FALSE. In this case, it's up to you. In a 12.2 version I set it to TRUE and
I had to intervene on several queries to set it locally to FALSE. You can
follow my example or do the opposite. You are free. But I'm sure you will
whatever value you’ll adopt for this parameter, I'm sure that you will
have to intervene locally to force the opposite value. in 19.3 I
adopted the opposite strategy
You can follow the PeopleSoft suggestion concerning the
_gby_hash_aggregation_enabled parameter
Best regards
Mohamed
Le mar. 18 janv. 2022 à 08:54, Lok P <loknath.73@xxxxxxxxx> a écrit :
You have not mentioned the current version of this Oracle database ?
Not sure of first_rows_1, however , I saw one thread in past as below, in
which "Mohamed Houri" mentioned that those three parameters were exactly
the ones suggested by peoplesoft to be changed :). So it might be that
first_row_1 is also peoplesoft suggested only and it may not be advisable
to play with that. Others may comment on this.
https://www.freelists.org/post/oracle-l/Simple-query-opting-higher-cost-path
On Tue, Jan 18, 2022 at 10:41 AM Pap <oracle.developer35@xxxxxxxxx>
wrote:
Hello Listers, We have a peoplesoft application database and almost all
the time we see the queries in the backend as above ~2000-3000+ lines with
multiple UNIONS in them. And the estimation seems really bad making us
confused many times but then we see the optimizer_mode has been set as
first_rows_1. Thus the indexed path is favored all the time even though few
of the queries perform better by forcing a full scan path. So I wanted to
check with experts here if those are really the recommended setups for
peoplesoft databases in general and thus should not be changed? During
encountering any performance issue many times we don't get the sql monitors
because of such long queries.
Along with above there are other parameters like _unnest_subquery,
_gby_hash_aggregation_enabled, _optimizer_skip_scan_enabled etc are set as
non default i.e. false.
Regards
Pap
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