Hello Sayan
Thanks for your answer. It confirms why I haven't experienced any performs
pain with cardinality feedback in all the 19c databases I have to deal
with. Until today where 6 critical queries changed their execution plan
from a good one to a very bad one and the non-sharing reason was
USE_FEEDBACK_STATS
Best regards
Mohamed
Le mar. 27 avr. 2021 à 14:20, Sayan Malakshinov <xt.and.r@xxxxxxxxx> a
écrit :
Hi Mohamed,
"_optimizer_use_feedback" works differently since 12.2 (and on 12.1.0.2
after the patch for bug# 22652097):
https://antognini.ch/2016/10/adaptive-query-optimization-configuration-parameters-preferences-and-fix-controls/
So it works pretty good now and with the disabled
OPTIMIZER_ADAPTIVE_STATISTICS by default, I do not change
_optimizer_use_feedback now.
If I need to fix some rare issues, I do that only for specific queries
using SQL profiles or patches.
On Tue, Apr 27, 2021 at 1:29 PM Mohamed Houri <mohamed.houri@xxxxxxxxx>
wrote:
Hello
In 11g and 12c, I used to disable the parameter _optimizer_use_feedback
because the re-optimization was always producing a suboptimal execution
plan. But I kept this parameter enabled while upgrading to 19c. And, after
more than 10 19c upgrades I haven’t noticed any performance issue induced
by the cardinality feedback feature. Until today, where a bunch of queries
changed their execution plan (from 1 second on average to 300 seconds)
because of cardinality feedback usage
Are you still disabling this feature in 19c?
Thanks
Mohamed Houri
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Best regards,
Sayan Malakshinov
Oracle performance tuning engineer
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