private Offset getStartOffset(ConcurrentSkipListMap<Offset, IndexSegment> indexSegments) {
    Offset startOffset;
    if (indexSegments.size() == 0) {
      LogSegment firstLogSegment = log.getFirstSegment();
      startOffset = new Offset(firstLogSegment.getName(), firstLogSegment.getStartOffset());
    } else {
      startOffset = indexSegments.firstKey();
    }
    return startOffset;
  }
Gets the start {@link Offset} of the given instance of  {@code indexSegments}.
@param indexSegments the map of index segment start {@link Offset} to {@link IndexSegment} instances
ambry-store/src/main/java/com/github/ambry/store/PersistentIndex.java