Postgres db Update to Version 15

Dear Postgres Team,

We are contacting you today to get your feedback on a service degradation, that occurred, after upgrading related postgres databases to db-Version 15.

We upgraded several Live- and Non-Live-Landscapes to db-Version 15, coming from db-version 11. One AWS-Live-Landscape showed an increasing CPU-Usage from 5 % to 100% with the effect, that Lifecycle Operations on customer side were experiencing intermittent availability issues several times and with a max period of 186 minutes of degradation.

The Root Cause of this behavior, as aligned with AWS RDS Support, has been a new feature-set coding (parallel_feature_query) with Postgres Version 15, that shows a different behavior due to related parameter (max_parallel_workers_per_gather).

This parameter sets the maximum number of workers, that can be started by a single Gather or Gather Merge node. Parallel workers are taken from the pool of processes established by max_worker_processes, limited by max_parallel_workers. The default value is 2. Setting this value to 0 disabled parallel query execution and resolved the issue.

Remaining question now is, what has to be done to move related Live-Landscapes back to the default parameter value (2) without creating the same impact again.

Did you see such behavior with other customers ?

What is your suggestion and recommended way-forward to enable parallel-worker setup again ?

Thanks and kind regards