code: function doSaveUpdate(datasetId, acknowledgementFields, callback) {
    debug('[%s] doSaveUpdate acknowledgementFields = %j' , datasetId, acknowledgementFields);
    var updatesCollection = mongoClient.collection(getDatasetUpdatesCollectionName(datasetId));
    updatesCollection.findOneAndUpdate({cuid: acknowledgementFields.cuid, hash: acknowledgementFields.hash}, {'$set': acknowledgementFields}, {upsert: true, returnOriginal: false}, function(err, updateResult) {
      if (err) {
        debugError('[%s] Failed to doSaveUpdate due to error %s :: acknowledgementFields = %j' ,datasetId,err,acknowledgementFields);
        return callback(err);
      }
      return callback(null, updateResult.value);
    });
  }
docs: Save the sync update to the `fhsync-<datasetId>-updates` collection
  
  @param {String} datasetId
  @param {storage~Acknowledgement} acknowledgementFields
  @param {Function} callback