I was just doing some benchmarking to check that IndexOrDocValues actually makes things faster when it is supposed to:
In the above results, the number after the query type indicates the percentage of docs in the index that it matches. With the baseline, range queries are simple point range queries, while the patch is an IndexOrDocValuesQuery that wraps both a point range query and a doc values query that matches the same documents. As expected, AndTerm35Range10 performs the same in both cases since the range is supposed to lead the iteration, so the IndexOrDocValuesQuery is rewritten to the wrapped point range query. However with AndTerm02Range25 the range cost is higher than the term cost so the range is only used for verifying matches and the IndexOrDocValuesQuery rewrites to the wrapped doc values query, yielding a speedup since we do not have to evaluate the range against the whole index.
I think the -2/-3% difference we are seeing for everything else than AndTerm02Range25 is noisy since term queries execute exactly the same way in both cases, yet they have this slight slowdown too.
I would like to make it easier to use by moving IndexOrDocValuesQuery and DocValuesRangeQuery to a different module than sandbox, and giving the doc values range query an API that is closer to point ranges by making the bounds required (null disallowed) and removing the includeLower and includeUpper parameters. I wanted to move to queries initially but maybe core is better, that way we could link from the point API to IndexOrDocValuesQuery as a way to make queries on fields that have both points and doc values more efficient.