Data center maintenance and drills
Planned maintenance or drills, exercises conducted to prepare personnel for potential emergencies or outages, can also affect query performance. Depending on the maintenance scope or drill scenario, some YDB nodes might become unavailable, which leads to the same impact as an outage.
Diagnostics
Check the planned maintenance and drills schedules to see if their timelines match with observed performance issues, otherwise, check the datacenter outage recommendations.
Recommendations
Contact the person responsible for the current maintenance or drill to discuss whether the performance impact is severe enough for it to be finished/canceled early, if possible.