public static long getTimestampInFileName(IChunkMetadata chunkMetaData) {
    IChunkLoader chunkLoader = chunkMetaData.getChunkLoader();
    if (chunkLoader instanceof DiskChunkLoader) {
      return ((DiskChunkLoader) chunkLoader).getTsFileID().getTimestamp();
    } else if (chunkLoader instanceof DiskAlignedChunkLoader) {
      return ((DiskAlignedChunkLoader) chunkLoader).getTsFileID().getTimestamp();
    } else {
      return Long.MAX_VALUE;
    }
  }
get the timestamp in file name of the chunk metadata.

@param chunkMetaData the corresponding ChunkMetadata in that file.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/operator/source/FileLoaderUtils.java