*** a/doc/src/sgml/protocol.sgml
--- b/doc/src/sgml/protocol.sgml
***************
*** 1039,1044 ****
--- 1039,1057 ----
      all columns in a given <command>COPY</> operation will use the same
      format, but the message design does not assume this.)
     </para>
+ 
+    <para>
+     There is another Copy-related mode called Copy-both, which allows
+     high-speed bulk data transfer to <emphasis>and</> from the server.
+     Copy-both mode is initiated when the backend with walsender mode
+     executes a <command>START_REPLICATION</command> statement.  The
+     backend sends a CopyBothResponse message to the frontend.  Both
+     the backend and the frontend should then send CopyData messages
+     between each other until the connection is terminated.  Copy-both
+     mode is used by streaming replication (see <xref
+     linkend="protocol-replication">).
+    </para>
+ 
    </sect2>
  
    <sect2 id="protocol-async">
***************
*** 1344,1350 **** The commands accepted in walsender mode are:
        WAL position <replaceable>XXX</>/<replaceable>XXX</>.
        The server can reply with an error, e.g. if the requested section of WAL
        has already been recycled. On success, server responds with a
!       CopyOutResponse message, and then starts to stream WAL to the frontend.
        WAL will continue to be streamed until the connection is broken;
        no further commands will be accepted.
       </para>
--- 1357,1363 ----
        WAL position <replaceable>XXX</>/<replaceable>XXX</>.
        The server can reply with an error, e.g. if the requested section of WAL
        has already been recycled. On success, server responds with a
!       CopyBothResponse message, and then starts to stream WAL to the frontend.
        WAL will continue to be streamed until the connection is broken;
        no further commands will be accepted.
       </para>
***************
*** 2696,2701 **** CopyOutResponse (B)
--- 2709,2750 ----
  
  <varlistentry>
  <term>
+ CopyBothResponse (B)
+ </term>
+ <listitem>
+ <para>
+ 
+ <variablelist>
+ <varlistentry>
+ <term>
+         Byte1('W')
+ </term>
+ <listitem>
+ <para>
+                 Identifies the message as a Start Copy Both response.
+                 This message is used only for Streaming Replication.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>
+         Int32
+ </term>
+ <listitem>
+ <para>
+                 Length of message contents in bytes, including self.
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ 
+ </para>
+ </listitem>
+ </varlistentry>
+ 
+ 
+ <varlistentry>
+ <term>
  DataRow (B)
  </term>
  <listitem>
*** a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
--- b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
***************
*** 50,55 **** static char *recvBuf = NULL;
--- 50,56 ----
  static bool libpqrcv_connect(char *conninfo, XLogRecPtr startpoint);
  static bool libpqrcv_receive(int timeout, unsigned char *type,
  				 char **buffer, int *len);
+ static void libpqrcv_send(const char *buffer, int nbytes);
  static void libpqrcv_disconnect(void);
  
  /* Prototypes for private functions */
***************
*** 64,73 **** _PG_init(void)
  {
  	/* Tell walreceiver how to reach us */
  	if (walrcv_connect != NULL || walrcv_receive != NULL ||
! 		walrcv_disconnect != NULL)
  		elog(ERROR, "libpqwalreceiver already loaded");
  	walrcv_connect = libpqrcv_connect;
  	walrcv_receive = libpqrcv_receive;
  	walrcv_disconnect = libpqrcv_disconnect;
  }
  
--- 65,75 ----
  {
  	/* Tell walreceiver how to reach us */
  	if (walrcv_connect != NULL || walrcv_receive != NULL ||
! 		walrcv_send != NULL || walrcv_disconnect != NULL)
  		elog(ERROR, "libpqwalreceiver already loaded");
  	walrcv_connect = libpqrcv_connect;
  	walrcv_receive = libpqrcv_receive;
+ 	walrcv_send = libpqrcv_send;
  	walrcv_disconnect = libpqrcv_disconnect;
  }
  
***************
*** 398,400 **** libpqrcv_receive(int timeout, unsigned char *type, char **buffer, int *len)
--- 400,417 ----
  
  	return true;
  }
+ 
+ /*
+  * Send a message to XLOG stream.
+  *
+  * ereports on error.
+  */
+ static void
+ libpqrcv_send(const char *buffer, int nbytes)
+ {
+ 	if (PQputCopyData(streamConn, buffer, nbytes) <= 0 ||
+ 		PQflush(streamConn))
+ 		ereport(ERROR,
+ 				(errmsg("could not send data to WAL stream: %s",
+ 						PQerrorMessage(streamConn))));
+ }
*** a/src/backend/replication/walreceiver.c
--- b/src/backend/replication/walreceiver.c
***************
*** 57,62 **** bool		am_walreceiver;
--- 57,63 ----
  /* libpqreceiver hooks to these when loaded */
  walrcv_connect_type walrcv_connect = NULL;
  walrcv_receive_type walrcv_receive = NULL;
+ walrcv_send_type walrcv_send = NULL;
  walrcv_disconnect_type walrcv_disconnect = NULL;
  
  #define NAPTIME_PER_CYCLE 100	/* max sleep time between cycles (100ms) */
***************
*** 247,253 **** WalReceiverMain(void)
  	/* Load the libpq-specific functions */
  	load_file("libpqwalreceiver", false);
  	if (walrcv_connect == NULL || walrcv_receive == NULL ||
! 		walrcv_disconnect == NULL)
  		elog(ERROR, "libpqwalreceiver didn't initialize correctly");
  
  	/*
--- 248,254 ----
  	/* Load the libpq-specific functions */
  	load_file("libpqwalreceiver", false);
  	if (walrcv_connect == NULL || walrcv_receive == NULL ||
! 		walrcv_send == NULL || walrcv_disconnect == NULL)
  		elog(ERROR, "libpqwalreceiver didn't initialize correctly");
  
  	/*
*** a/src/backend/replication/walsender.c
--- b/src/backend/replication/walsender.c
***************
*** 287,296 **** WalSndHandshake(void)
  									(errcode(ERRCODE_CANNOT_CONNECT_NOW),
  									 errmsg("standby connections not allowed because wal_level=minimal")));
  
! 						/* Send a CopyOutResponse message, and start streaming */
! 						pq_beginmessage(&buf, 'H');
! 						pq_sendbyte(&buf, 0);
! 						pq_sendint(&buf, 0, 2);
  						pq_endmessage(&buf);
  						pq_flush();
  
--- 287,294 ----
  									(errcode(ERRCODE_CANNOT_CONNECT_NOW),
  									 errmsg("standby connections not allowed because wal_level=minimal")));
  
! 						/* Send a CopyBothResponse message, and start streaming */
! 						pq_beginmessage(&buf, 'W');
  						pq_endmessage(&buf);
  						pq_flush();
  
*** a/src/include/replication/walreceiver.h
--- b/src/include/replication/walreceiver.h
***************
*** 84,89 **** typedef bool (*walrcv_receive_type) (int timeout, unsigned char *type,
--- 84,92 ----
  												 char **buffer, int *len);
  extern PGDLLIMPORT walrcv_receive_type walrcv_receive;
  
+ typedef void (*walrcv_send_type) (const char *buffer, int nbytes);
+ extern PGDLLIMPORT walrcv_send_type walrcv_send;
+ 
  typedef void (*walrcv_disconnect_type) (void);
  extern PGDLLIMPORT walrcv_disconnect_type walrcv_disconnect;
  
*** a/src/interfaces/libpq/fe-exec.c
--- b/src/interfaces/libpq/fe-exec.c
***************
*** 1586,1591 **** PQgetResult(PGconn *conn)
--- 1586,1592 ----
  				res = PQmakeEmptyPGresult(conn, PGRES_COPY_IN);
  			break;
  		case PGASYNC_COPY_OUT:
+ 		case PGASYNC_COPY_BOTH:
  			if (conn->result && conn->result->resultStatus == PGRES_COPY_OUT)
  				res = pqPrepareAsyncResult(conn);
  			else
***************
*** 2000,2006 **** PQnotifies(PGconn *conn)
  }
  
  /*
!  * PQputCopyData - send some data to the backend during COPY IN
   *
   * Returns 1 if successful, 0 if data could not be sent (only possible
   * in nonblock mode), or -1 if an error occurs.
--- 2001,2007 ----
  }
  
  /*
!  * PQputCopyData - send some data to the backend during COPY IN or COPY BOTH
   *
   * Returns 1 if successful, 0 if data could not be sent (only possible
   * in nonblock mode), or -1 if an error occurs.
***************
*** 2010,2016 **** PQputCopyData(PGconn *conn, const char *buffer, int nbytes)
  {
  	if (!conn)
  		return -1;
! 	if (conn->asyncStatus != PGASYNC_COPY_IN)
  	{
  		printfPQExpBuffer(&conn->errorMessage,
  						  libpq_gettext("no COPY in progress\n"));
--- 2011,2018 ----
  {
  	if (!conn)
  		return -1;
! 	if (conn->asyncStatus != PGASYNC_COPY_IN &&
! 		conn->asyncStatus != PGASYNC_COPY_BOTH)
  	{
  		printfPQExpBuffer(&conn->errorMessage,
  						  libpq_gettext("no COPY in progress\n"));
***************
*** 2148,2153 **** PQputCopyEnd(PGconn *conn, const char *errormsg)
--- 2150,2156 ----
  
  /*
   * PQgetCopyData - read a row of data from the backend during COPY OUT
+  * or COPY BOTH
   *
   * If successful, sets *buffer to point to a malloc'd row of data, and
   * returns row length (always > 0) as result.
***************
*** 2161,2167 **** PQgetCopyData(PGconn *conn, char **buffer, int async)
  	*buffer = NULL;				/* for all failure cases */
  	if (!conn)
  		return -2;
! 	if (conn->asyncStatus != PGASYNC_COPY_OUT)
  	{
  		printfPQExpBuffer(&conn->errorMessage,
  						  libpq_gettext("no COPY in progress\n"));
--- 2164,2171 ----
  	*buffer = NULL;				/* for all failure cases */
  	if (!conn)
  		return -2;
! 	if (conn->asyncStatus != PGASYNC_COPY_OUT &&
! 		conn->asyncStatus != PGASYNC_COPY_BOTH)
  	{
  		printfPQExpBuffer(&conn->errorMessage,
  						  libpq_gettext("no COPY in progress\n"));
*** a/src/interfaces/libpq/fe-protocol2.c
--- b/src/interfaces/libpq/fe-protocol2.c
***************
*** 541,546 **** pqParseInput2(PGconn *conn)
--- 541,550 ----
  				case 'H':		/* Start Copy Out */
  					conn->asyncStatus = PGASYNC_COPY_OUT;
  					break;
+ 					/*
+ 					 * Don't need to process CopyBothResponse here because
+ 					 * it never arrives from the server during protocol 2.0.
+ 					 */
  				default:
  					printfPQExpBuffer(&conn->errorMessage,
  									  libpq_gettext(
*** a/src/interfaces/libpq/fe-protocol3.c
--- b/src/interfaces/libpq/fe-protocol3.c
***************
*** 358,363 **** pqParseInput3(PGconn *conn)
--- 358,375 ----
  					conn->asyncStatus = PGASYNC_COPY_OUT;
  					conn->copy_already_done = 0;
  					break;
+ 				case 'W':		/* Start Copy Both */
+ 					/*
+ 					 * We don't need to use getCopyStart here since CopyBothResponse
+ 					 * specifies neither the copy format nor the number of columns in
+ 					 * the Copy data. They should be always zero.
+ 					 */
+ 					conn->result = PQmakeEmptyPGresult(conn, PGRES_COPY_OUT);
+ 					if (!conn->result)
+ 						return;
+ 					conn->asyncStatus = PGASYNC_COPY_BOTH;
+ 					conn->copy_already_done = 0;
+ 					break;
  				case 'd':		/* Copy Data */
  
  					/*
*** a/src/interfaces/libpq/libpq-int.h
--- b/src/interfaces/libpq/libpq-int.h
***************
*** 218,224 **** typedef enum
  	PGASYNC_BUSY,				/* query in progress */
  	PGASYNC_READY,				/* result ready for PQgetResult */
  	PGASYNC_COPY_IN,			/* Copy In data transfer in progress */
! 	PGASYNC_COPY_OUT			/* Copy Out data transfer in progress */
  } PGAsyncStatusType;
  
  /* PGQueryClass tracks which query protocol we are now executing */
--- 218,225 ----
  	PGASYNC_BUSY,				/* query in progress */
  	PGASYNC_READY,				/* result ready for PQgetResult */
  	PGASYNC_COPY_IN,			/* Copy In data transfer in progress */
! 	PGASYNC_COPY_OUT,			/* Copy Out data transfer in progress */
! 	PGASYNC_COPY_BOTH			/* Copy In/Out data transfer in progress */
  } PGAsyncStatusType;
  
  /* PGQueryClass tracks which query protocol we are now executing */