Faster Performance for Multi-Component Indices with Parameterized Queries

When the key to search for was not known, certain logic (a function determining an "average" selectivity for an index) was written such that the function was not called if there was a multi-component index and not all components were specified. However, if this condition failed, the call was not made and a selectivity of 1 was obtained, which resulted in the index to be considered a poor choice. In fact, the index was considered a worst case scenario and avoided.

This logic has been changed such that the function is always called when the key to search for is not known, and should this call fail, then an optional default value is set instead.