code: public FSDataOutputStream append (Path p, final int bufferSize, Progressable progress) throws IOException {
      try (Closeable context = new TimerContextWithLog(this.appendTimer.time(), "append", p)) {
        return super.append(p, bufferSize, progress);
      }
    }
docs: Add timer metrics to {@link DistributedFileSystem#append(Path, int, Progressable)}