Author:     Noah Misch <noah@leadboat.com>
Commit:     Noah Misch <noah@leadboat.com>

    (not for commit) Reproduce failure seen here:
    
    https://postgr.es/m/CAEepm=1MzM2Z_xNe4foGwZ1a+MO_2S9oYDq3M5D11=JDU_+0Nw@mail.gmail.com
    https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=frogfish&dt=2020-03-07%2018%3A49%3A34

diff --git a/src/backend/libpq/pqcomm.c b/src/backend/libpq/pqcomm.c
index 7717bb2..2268009 100644
--- a/src/backend/libpq/pqcomm.c
+++ b/src/backend/libpq/pqcomm.c
@@ -1448,7 +1448,8 @@ internal_flush(void)
 				last_reported_send_errno = errno;
 				ereport(COMMERROR,
 						(errcode_for_socket_access(),
-						 errmsg("could not send data to client: %m")));
+						 errmsg("could not send data to client: %m"),
+						 errbacktrace()));
 			}
 
 			/*
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index ae4a9cb..d660038 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1229,6 +1229,19 @@ WalSndWriteData(LogicalDecodingContext *ctx, XLogRecPtr lsn, TransactionId xid,
 	if (pq_flush_if_writable() != 0)
 		WalSndShutdown();
 
+	/*
+	 * If this XLogData message causes pg_recvlogical to reach its --endpos,
+	 * pg_recvlogical will exit during this sleep.
+	 */
+	pg_usleep(15 * 1000);
+	/*
+	 * Send a long NoticeResponse.  If the peer has exited, internal_flush()
+	 * will observe EPIPE and ereport(COMMERROR).
+	 */
+	elog(WARNING, "long notice %065535d", 7);
+	if (pq_flush_if_writable() != 0)
+		WalSndShutdown();
+
 	/* Try taking fast path unless we get too close to walsender timeout. */
 	if (now < TimestampTzPlusMilliseconds(last_reply_timestamp,
 										  wal_sender_timeout / 2) &&