private void analyze() throws IOException {
    try {
      snapshotId = reader.readLine();
      String line;
      while ((line = reader.readLine()) != null && !line.equals(SnapshotLogger.END_FLAG)) {
        fileInfoSet.add(line);
      }
      complete = line != null;
    } finally {
      reader.close();
    }
  }
Return the total num of file in this snapshot.

@return
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/dataregion/snapshot/SnapshotLogAnalyzer.java