code: def _index_nonsharded_search(self, index_file, xq, nprobe):
      assert nprobe is not None
      logging.info(f"index {index_file}")
      assert os.path.exists(
          index_file
      ), f"file {index_file} does not exist "
      index = faiss.read_index(
          index_file, faiss.IO_FLAG_ONDISK_SAME_DIR
      )
      logging.info(f"index size {index.ntotal} ")
      index_ivf = faiss.downcast_index(faiss.extract_index_ivf(index))
      logging.info(f"setting nprobe to {nprobe}")
      index_ivf.nprobe = nprobe
      return index.search(xq, self.k)
  
imports: import faiss
  import numpy
  import os
  from tqdm import tqdm, trange
  import sys
  import logging
  from faiss.contrib.ondisk import merge_ondisk
  from faiss.contrib.big_batch_search import big_batch_search
  from faiss.contrib.exhaustive_search import knn_ground_truth
  from faiss.contrib.evaluation import knn_intersection_measure
  from utils import get_intersection_cardinality_frequencies, margin, is_pretransform_index
  from dataset import create_dataset_from_oivf_config
label_desc: Use image node_id 11 for calling the OfflineIVF obj's underlying member method code with example usage: obj._index_nonsharded_search(index_file, xq, nprobe) and returns: index