Looking at
http://www.postgresql.org/docs/devel/static/protocol-replication.html
under START_REPLICATION it goes
"""
The payload of each CopyData message from server to the client contains
a message of one of the following formats:
If a slot's name is provided via slotname, it will be updated as
replication progresses so that the server knows which WAL segments - and
if hot_standby_feedback is on which transactions - are still needed by
the standby.
XLogData (B)
...
Primary keepalive message (B)
...
"""
That second paragraph was inserted recently and doesn't make sense
there. It should be moved somewhere else.
More generally, it is weird that the message formats are described
there, even though the rest of the protocol documentation only mentions
the messages by name and then describes the formats later
(http://www.postgresql.org/docs/devel/static/protocol-message-types.html
and
http://www.postgresql.org/docs/devel/static/protocol-message-formats.html).For example, the meaning of the "(B)" code
isn'tdescribed until two
sections later.
I think the description of the details of the these messages should also
be moved there. The CopyBothResponse, which is also used for
replication only, is also listed among the "normal" message formats.