private boolean loadIndex(long dataIndexVersion) throws IOException {
   mIndexPos = 0;
   mIndexedSequenceFileNumber = -1;
   mIndex =
       DataFileIndex.loadDataFileIndex(
           dataIndexVersion, new File(mDir, mIndexFile), mDataFilePrefix);
   if (mIndex.getTotalNumberSequences() != mNumberSequences) {
     throw new CorruptSdfException(mDir);
   }
   return true;
 }