public static long parseStartSearchIndex(String filename) {
    Matcher matcher = WAL_FILE_NAME_PATTERN.matcher(filename);
    if (matcher.find()) {
      return Long.parseLong(matcher.group(WAL_START_SEARCH_INDEX));
    }
    throw new RuntimeException("Invalid wal file name: " + filename);
  }
Parse start search index from filename.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/dataregion/wal/utils/WALFileUtils.java