Sometimes, like in HELP-69798, we suspect that the issues have little or nothing to do with planning time but we cannot really confidently tell since we have not enough visibility metrics into the planner. Therefore we should add FTDC metrics for:

Number of keys not found vs found but inactive vs found and active in plan cache
Time waiting for the partitioned cache lock
Time spent retrieving a plan from cache

– Do note that this is a series of tickets to increase visibility. These tickets are sliced to be able to be delivered in a timely manner.