The PlanStage class provides a getStats() method to allow the derived classes (e.g. index_scan, collection_scan etc.) to collect statistics about their specific execution.
The various runners (SingleSolution, CachedRunner etc.) call getStats() in the getExplainPlan implementation. However, the details collection by each concrete implementation are not projected in the explain plan.
This could provide core development/debug information as well as help customer support scenarios.
Enable the dumping out of the getStats() output into the explain plan.
To view the stats from the shell, use db.col.find().explain(true)