One of our colleagues in his project was facing issues with the "delayed
block cleanout" effect i.e. lot many queries were struggling with
"Transaction table consistent read- undo record applied " after migrating
from 11.2 version to 12.1 with the same workload commit frequency. And
after discussion with Oracle, they concluded it was a buggy behaviour
associated with AUTO UNDO management on 12.1 which was not allowing enough
undo segments asper the rate of increase in number of transactions and so
they endup setting that underscore parameter value to specific value( I
think it was ~2000) as per Oracle suggestion. So I think it should be some
number based on the number of transaction count patterns. Or say based on
ONLINE and OFFLINE count in dba_rollback_segs. And i have not heard of any
negative effects from him after doing this but as its a hidden/underscore
parameter so better ask for oracle guidance about the proper value.
Regards
Lok
On Tue, Apr 20, 2021 at 10:28 AM Laurentiu Oprea <
laurentiu.oprea06@xxxxxxxxx> wrote:
Hello,
DB Version: 12.1
Is someone played around with parameter _rollback_segment_count ? I`m most
interested in what are the side effects of increasing this parameter.
Thank you.
