In SERVER-119883 we introduced internalEnableJoinOptimizationUseIndexUniqueness defaulting to off. The optimization uses uniqueness information derived from indexes to better estimate the selectivity of join predicates. We default it to off to ensure we have test/perf coverage of NDV estimation using method of moments - this actually allowed us to identify and fix SERVER-123652.

However, in production this knob should be enabled, but we need to think about how to keep sufficient test coverage for method of moments. TPC-H/E workloads have unique indexes, so during this ticket may require our method of moments coverage. Although after SERVER-123652, defacto unique fields without a unqiue constraint will be treated as if they were unique, so perhaps this is less of an issue.