@Override
    public void shuffle() {
      // do nothing
      if (LOGGER.isDebugEnabled()) {
        LOGGER.debug(
            "PlainShuffleStrategy needs to do nothing, current channel index is {}",
            downStreamChannelIndex.getCurrentIndex());
      }
    }
SinkHandle may have multiple channels. we need to choose the next channel each time we send a
TsBlock.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/exchange/sink/ShuffleSinkHandle.java