code: public void retriggerPartitionRequest(IntermediateResultPartitionID partitionId) throws IOException, InterruptedException {
  		synchronized (requestLock) {
  			if (!isReleased) {
  				final InputChannel ch = inputChannels.get(partitionId);
  
  				checkNotNull(ch, "Unknown input channel with ID " + partitionId);
  
  				LOG.debug("{}: Retriggering partition request {}:{}.", owningTaskName, ch.partitionId, consumedSubpartitionIndex);
  
  				if (ch.getClass() == RemoteInputChannel.class) {
  					final RemoteInputChannel rch = (RemoteInputChannel) ch;
  					rch.retriggerSubpartitionRequest(consumedSubpartitionIndex);
  				}
  				else if (ch.getClass() == LocalInputChannel.class) {
  					final LocalInputChannel ich = (LocalInputChannel) ch;
  
  					if (retriggerLocalRequestTimer == null) {
  						retriggerLocalRequestTimer = new Timer(true);
  					}
  
  					ich.retriggerSubpartitionRequest(retriggerLocalRequestTimer, consumedSubpartitionIndex);
  				}
  				else {
  					throw new IllegalStateException(
  							"Unexpected type of channel to retrigger partition: " + ch.getClass());
  				}
  			}
  		}
  	}
docs: Retriggers a partition request.