@VisibleForTesting
  int getNumAliveFetchers() {
    return splitFetcherManager.getNumAliveFetchers();
  }
The source reader for Kafka partitions.
amoro-format-mixed/amoro-mixed-flink/amoro-mixed-flink-common/src/main/java/org/apache/amoro/flink/read/internals/KafkaSourceReader.java