This is an expensive call which reconstructs a full PlanStats tree. However, we only need a single metric from this tree which represents a total number of storage reads performed during PlanStage tree execution and computed with calculateNumberOfReads().

However, it seems there is a cheaper way to get this number. We can use accumulate() to populate a PlanSummaryStats instance off the PlanStage's common stats without constructing a PlanStats tree. Then we can sum up totalKeysExamined and totalDocsExamined to get the total number of storage reads.