lib/storage/dataset-clients.js
function createIndexForCollection(collectionName, indexField, indexOpts) {
  var collection = mongoClient.collection(collectionName);
  collection.createIndex(indexField, indexOpts, function(err) {
    if (err) {
      debugError('Failed to create index for collection. collection = %s :: index = %j :: error = %j',collectionName,indexField,err);
    } else {
      debug('Index created for collection. Collection = %s  :: index = %j',collectionName,indexField);
    }
  });
}
function createIndexForCollection(collectionName, indexField, indexOpts) {
  var collection = mongoClient.collection(collectionName);
  collection.createIndex(indexField, indexOpts, function(err) {
    if (err) {
      debugError('Failed to create index for collection. collection = %s :: index = %j :: error = %j',collectionName,indexField,err);
    } else {
      debug('Index created for collection. Collection = %s  :: index = %j',collectionName,indexField);
    }
  });
}
Create an index on the given collection
@param {String} collectionName
@param {Object} indexField see mongodb indexes
@param {Object} indexOpts see mongodb indexes options