*** 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/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
***************
*** 2002,2007 **** PQnotifies(PGconn *conn)
--- 2002,2010 ----
  /*
   * PQputCopyData - send some data to the backend during COPY IN
   *
+  * This function can be called by walreceiver even during COPY OUT
+  * to send a message to the master.
+  *
   * 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"));
--- 2013,2020 ----
  {
  	if (!conn)
  		return -1;
! 	if (conn->asyncStatus != PGASYNC_COPY_IN &&
! 		conn->asyncStatus != PGASYNC_COPY_OUT)
  	{
  		printfPQExpBuffer(&conn->errorMessage,
  						  libpq_gettext("no COPY in progress\n"));