[Twisted-Python] Clarification or pausing a consumer

I have a app that needs to send data as an http response. But the data is produced slowly. More slowly then the time taken to transmit it. The consumer keeps calling resumeProducing, but there is no data to send often. What is the correct way to pause the consumer so that it does not keep calling resumeProducing? unregisterProducer? Then when the next block of data is available what is the correct way to resume the consumer? registerProducer? Related to that why does HTTPChannel.registerProducer convert a IPullProducer into a IPushProducer using _PullToPush? Barry