Looking at ProtobufLogWriter class, it looks like the call to flush() in
the sync method is a noop.
The underlying output stream is DFSOutputStream, which doesn't implement
And, it calls sync() anyway, which ensures the data is written to DN's
Previously with SequenceFile$Writer, it writes data to the outputstream
(using Writables#write), and invoke sync/hflush.
Is there a reason we have this call here? Please let me know if I miss any