The 'planCacheListPlans' command (https://docs.mongodb.com/manual/reference/command/planCacheListPlans/#dbcmd.planCacheListPlans) and 'planCacheListQueryShapes' command (https://docs.mongodb.com/manual/reference/command/planCacheListQueryShapes/#dbcmd.planCacheListQueryShapes) have been removed from the code base. They were deprecated in 4.2, and will be removed entirely in 4.4. We should note this in the 4.4 compatibility documentation, and also remove the reference pages. We expect users to migrate to the $planCacheStats aggregation source (https://docs.mongodb.com/manual/reference/operator/aggregation/planCacheStats/).

There are also changes to the plan cache helpers in the shell that need to be documented. The PlanCache.getPlansByQuery() shell helper (https://docs.mongodb.com/manual/reference/method/PlanCache.getPlansByQuery/#PlanCache.getPlansByQuery) has been deleted. Similarly, PlanCache.listQueryShapes() was deleted (https://docs.mongodb.com/manual/reference/method/PlanCache.listQueryShapes/#PlanCache.listQueryShapes).

Finally, this change adds a new plan cache helper to the shell called PlanCache.list(). It is sugar for $planCacheStats. It can be invoked as db.myCollection.getPlanCache().list() in order to obtain the entire contents of the plan cache for 'myCollection'. It optionally accepts a pipeline that can be used to transform the plan cache metadata using MQL, e.g. db.myCollection.getPlanCache().list([{$match: {queryHash: <hash>}}]).

I don't think drivers changes will be needed, but I'm clicking the box just in case so that they get notified of this change. As far as I know, only the shell implements helpers for the plan cache commands.