Does HDFS enable a customer to peruse a record, which is already opened for writing?

Yes, one can read the document, which is as of already opened. However, the issue in perusing a document which is right now being composed lies in the consistency of the information, i.e. HDFS does not give the surety that the information which has been built into the document will be visible to another reader before the document has been closed down. For this, one can call the hflush activity explicitly which will drive all of the information in the cushion into the composed pipeline and afterward the hflush task will wait for the affirmations from the DataNodes.