Applications tend to read sequently. So the normal process is, the
  app reads some bit, then venus asks the next block from the server,
  if the server's reply received the app gets its data, then it 
  reads the next data and so on.

Venus does whole-file caching, so this doesn't make sense.  The open
doesn't finish until the whole file has been obtained.

The RPC2 protocol does not stream particularly well on slow links, but
that's a separate issue.