Major Description
HDFS write is asynchronous and data may not be available to read immediately after write.
One of the main reason is that DFSClient doesn't flush data to DN until its local buffer is full.
To workaround this problem, when a read comes after write to the same file, NFS gateway should sync the data so the read request can get the latest content. The drawback is that, the frequent hsync() call can slow down data write.