And one other thought: we could also add new max/min lat/lon fields to the cell table and maintain those as part of the cell_location_update code. That code reads the old existing value and only ever works on getting a couple of new measures at a time. Comparing those couple of new records against the existing max/min values is easy and cheap; no need to go back to cell_measure and look at all the values.

Using these max/min lat/lon fields can also later be used to improve the reported accuracy in the search API. Currently we always report the worst case (35km). If we have an estimate of the maximum cell size, we can lower that accuracy number.