public ElephantBackfillFetcher getBackfillFetcherForApplicationType(ApplicationType type) {
    ElephantFetcher fetcher = _typeToFetcher.get(type);
    if (fetcher instanceof ElephantBackfillFetcher) {
      return (ElephantBackfillFetcher) fetcher;
    }
    return null;
  }
Given an application type, return the currently ElephantFetcher that binds with the type.

@param type The application type
@return The corresponding fetcher
app/com/linkedin/drelephant/ElephantContext.java