We have seen cases where the multi plan runner cannot distinguish between index intersection and single index plans. For instance, if the query has zero results, then all plans could be equally unproductive, and we have no information to distinguish between the various plans (see SERVER-12639). The ixisect plan might be chosen even if it is dramatically slower than the other plans.

We should penalize ixisect plans and require them to make up the delta with a no-fetch bonus.