From 508199bc4b245f834911d71a55e3215997c06ae6 Mon Sep 17 00:00:00 2001
From: Tatsuo Ishii <ishii@sraoss.co.jp>
Date: Thu, 16 Sep 2021 15:44:51 +0900
Subject: [PATCH] Fix occasional hang in COPY FROM.

If an error occurs while doing COPY FROM, it was possible the
Pgpool-II waited forever for a response from backend after COPY end
marker was sent from frontend. Pgpool expected a new message arrives
to socket, but it is possible that the message (in this case an error
message) is already in the backend read buffer. The fix is, check the
buffer is empty or not before reading from the socket.
New test case (07.copy_hang) is also added.

The bug was found by Bo Peng.
---
 src/protocol/pool_proto_modules.c             | 14 ++++-
 .../regression/tests/076.copy_hang/test.sh    | 54 +++++++++++++++++++
 2 files changed, 67 insertions(+), 1 deletion(-)
 create mode 100755 src/test/regression/tests/076.copy_hang/test.sh

diff --git a/src/protocol/pool_proto_modules.c b/src/protocol/pool_proto_modules.c
index f1111b0c8..f95a49d80 100644
--- a/src/protocol/pool_proto_modules.c
+++ b/src/protocol/pool_proto_modules.c
@@ -57,6 +57,7 @@
 #include "utils/pool_stream.h"
 #include "utils/ps_status.h"
 #include "utils/pool_signal.h"
+#include "utils/pool_ssl.h"
 #include "utils/palloc.h"
 #include "utils/memutils.h"
 #include "query_cache/pool_memqcache.h"
@@ -3306,6 +3307,9 @@ CopyDataRows(POOL_CONNECTION * frontend,
 		}
 	}
 
+	/*
+	 * Wait till backend responds
+	 */
 	if (copyin)
 	{
 		for (i = 0; i < NUM_BACKENDS; i++)
@@ -3314,7 +3318,15 @@ CopyDataRows(POOL_CONNECTION * frontend,
 			{
 				pool_flush(CONNECTION(backend, i));
 
-				if (synchronize(CONNECTION(backend, i)))
+				/*
+				 * Check response from the backend.  First check SSL and read
+				 * buffer of the backend. It is possible that there's an error
+				 * message in the buffer if the COPY command went wrong.
+				 * Otherwise wait for data arrival to the backend socket.
+				 */
+				if (!pool_ssl_pending(CONNECTION(backend, i)) &&
+					pool_read_buffer_is_empty(CONNECTION(backend, i)) &&
+					synchronize(CONNECTION(backend, i)))
 					ereport(FATAL,
 							(return_code(2),
 							 errmsg("unable to copy data rows"),
diff --git a/src/test/regression/tests/076.copy_hang/test.sh b/src/test/regression/tests/076.copy_hang/test.sh
new file mode 100755
index 000000000..2abe488ed
--- /dev/null
+++ b/src/test/regression/tests/076.copy_hang/test.sh
@@ -0,0 +1,54 @@
+#!/usr/bin/env bash
+#-------------------------------------------------------------------
+# test script for copy plus error case.
+# It was reported that following sequece of copy command cause psql hang.
+#
+# CREATE TEMP TABLE vistest (a text);  
+# COPY vistest FROM stdin CSV FREEZE;
+# Enter data to be copied followed by a newline.
+# End with a backslash and a period on a line by itself, or an EOF signal.
+# >> p
+# >> g
+# >> \.
+#
+# In the normal case an error should be returned to psql.
+#ERROR:  cannot perform COPY FREEZE because the table was not created or truncated in the current subtransaction
+
+source $TESTLIBS
+TESTDIR=testdir
+PSQL=$PGBIN/psql
+
+rm -fr $TESTDIR
+mkdir $TESTDIR
+cd $TESTDIR
+
+# create test environment
+echo -n "creating test environment..."
+$PGPOOL_SETUP -n 3 || exit 1
+echo "done."
+
+source ./bashrc.ports
+
+export PGPORT=$PGPOOL_PORT
+
+./startall
+wait_for_pgpool_startup
+
+# execute COPY
+
+timeout 10 $PSQL test <<EOF
+CREATE TEMP TABLE vistest (a text);  
+COPY vistest FROM stdin CSV FREEZE;
+p
+g
+\\.
+\\q
+EOF
+
+if [ ! $? -eq 0 ];then
+    echo ...timed out.
+    ./shutdownall
+    exit 1
+fi
+echo ...ok.
+./shutdownall
-- 
2.39.5