code: void retriggerSubpartitionRequest(int subpartitionIndex) throws IOException, InterruptedException {
  		checkState(partitionRequestClient != null, "Missing initial subpartition request.");
  
  		if (increaseBackoff()) {
  			partitionRequestClient.requestSubpartition(
  				partitionId, subpartitionIndex, this, getCurrentBackoff());
  		} else {
  			failPartitionRequest();
  		}
  	}
docs: Retriggers a remote subpartition request.