Tflush tag  oldtag  Rflush tag 
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. The response to a Tflush message should never be 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.
The following exceptional conditions are handled correctly by the above specification: