message: Reduce vector reallocations in diverse columns (TRIVIAL)
diff: @@ -83,6 +83,16 @@ getIndex(CellValue & val)
  index = indexedVals.size();
  lastValue = val;
  valueIndex[hash] = index;
  +
  + // If it looks like each value is in fact distinct or close to that,
  + // then we reserve enough capacity to ensure we don't continually
  + // reallocate the vector.
  + if (indexedVals.size() == indexedVals.capacity()
  + && indexedVals.size() > 32
  + && indexedVals.size() * 2 >= sparseIndexes.size()) {
  + indexedVals.reserve(sparseIndexes.capacity());
  + }
  +
  indexedVals.emplace_back(std::move(val));
  }
  else {
  