FLUSH(5)                                                 FLUSH(5)

          flush - abort a message

          Tflush  tag[2] oldtag[2]
          Rflush  tag[2]

          When the response to a request is no longer needed, such as
          when a user interrupts a process doing a read(2), a Tflush
          request is sent to the server to purge the pending response.
          The message being flushed is identified by oldtag. The
          semantics of flush depends on messages arriving in order.

          The server must answer the flush message immediately.  If it
          recognizes oldtag as the tag of a pending transaction, it
          should abort any pending response and discard that tag.  In
          either case, it should respond with an Rflush echoing the
          tag (not oldtag) of the Tflush message.  A Tflush can never
          be responded to by an Rerror message.

          When the client sends the Tflush, it should disregard all
          messages received with tag oldtag until the corresponding
          Rflush is received, at which point oldtag may be recycled
          for subsequent messages.

          Several exceptional conditions are handled correctly by the
          above specification: sending multiple flushes for a single
          tag, flushing a Tflush, and flushing an invalid tag.