static String generateIndexSegmentFilenamePrefix(Offset startOffset) {
    LogSegmentName logSegmentName = startOffset.getName();
    StringBuilder filenamePrefix = new StringBuilder(logSegmentName.toString());
    if (!logSegmentName.isSingleSegment()) {
      filenamePrefix.append(BlobStore.SEPARATOR);
    }
    return filenamePrefix.append(startOffset.getOffset()).append(BlobStore.SEPARATOR).toString();
  }
Creates the prefix for the index segment file name.
@param startOffset The start {@link Offset} in the {@link Log} that this segment represents.
@return the prefix for the index segment file name (also used for bloom filter file name).
ambry-store/src/main/java/com/github/ambry/store/IndexSegment.java