code: def WriteBlobs(self, blob_id_data_map):
      
  
      urns = {self._BlobUrn(blob_id): blob_id for blob_id in blob_id_data_map}
  
      mutation_pool = data_store.DB.GetMutationPool()
  
      existing = aff4.FACTORY.MultiOpen(
          urns, aff4_type=aff4.AFF4MemoryStreamBase, mode="r")
  
      for blob_urn, blob_id in iteritems(urns):
        if blob_urn in existing:
          logging.debug("Blob %s already stored.", blob_id)
          continue
  
        with aff4.FACTORY.Create(
            blob_urn,
            aff4.AFF4UnversionedMemoryStream,
            mode="w",
            mutation_pool=mutation_pool) as fd:
          content = blob_id_data_map[blob_id]
          fd.Write(content)
  
        logging.debug("Got blob %s (length %s)", blob_id.AsHexString(),
                      len(content))
  
      mutation_pool.Flush()
docs: Creates or overwrites blobs.