pg_upgrade: Use max_protocol_version=3.0 for older servers

The grease patch in 4966bd3ed found its first problem: prior to the
February 2018 patch releases, no server knew how to negotiate protocol
versions, so pg_upgrade needs to take that into account when speaking to
those older servers.

This will be true even after the grease feature is reverted; we don't
need anyone to trip over this again in the future. Backpatch so that all
supported versions of pg_upgrade can gracefully handle an update to the
default protocol version. (This is needed for any distributions that
link older binaries against newer libpqs, such as Debian.) Branches
prior to 18 need an additional version check, for the existence of
max_protocol_version.

Per buildfarm member crake.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CAOYmi%2B%3D4QhCjssfNEoZVK8LPtWxnfkwT5p-PAeoxtG9gpNjqOQ%40mail.gmail.com
Backpatch-through: 14

src/bin/pg_upgrade/dump.c

@@ -21,9 +21,10 @@ generate_old_dump(void)
 
 	/* run new pg_dumpall binary for globals */
 	exec_prog(UTILITY_LOG_FILE, NULL, true, true,
-			  "\"%s/pg_dumpall\" %s --globals-only --quote-all-identifiers "
+			  "\"%s/pg_dumpall\" %s%s --globals-only --quote-all-identifiers "
 			  "--binary-upgrade %s --no-sync -f \"%s/%s\"",
 			  new_cluster.bindir, cluster_conn_opts(&old_cluster),
+			  protocol_negotiation_supported(&old_cluster) ? "" : " -d \"max_protocol_version=3.0\"",
 			  log_opts.verbose ? "--verbose" : "",
 			  log_opts.dumpdir,
 			  GLOBALS_DUMP_FILE);
@@ -43,6 +44,9 @@ generate_old_dump(void)
 		initPQExpBuffer(&connstr);
 		appendPQExpBufferStr(&connstr, "dbname=");
 		appendConnStrVal(&connstr, old_db->db_name);
+		if (!protocol_negotiation_supported(&old_cluster))
+			appendPQExpBufferStr(&connstr, " max_protocol_version=3.0");
+
 		initPQExpBuffer(&escaped_connstr);
 		appendShellString(&escaped_connstr, connstr.data);
 		termPQExpBuffer(&connstr);

src/bin/pg_upgrade/pg_upgrade.h

@@ -501,6 +501,7 @@ unsigned int str2uint(const char *str);
 /* version.c */
 
 bool		jsonb_9_4_check_applicable(ClusterInfo *cluster);
+bool		protocol_negotiation_supported(const ClusterInfo *cluster);
 void		old_9_6_invalidate_hash_indexes(ClusterInfo *cluster,
 											bool check_mode);
 

src/bin/pg_upgrade/server.c

@@ -71,6 +71,8 @@ get_db_conn(ClusterInfo *cluster, const char *db_name)
 		appendPQExpBufferStr(&conn_opts, " host=");
 		appendConnStrVal(&conn_opts, cluster->sockdir);
 	}
+	if (!protocol_negotiation_supported(cluster))
+		appendPQExpBufferStr(&conn_opts, " max_protocol_version=3.0");
 
 	conn = PQconnectdb(conn_opts.data);
 	termPQExpBuffer(&conn_opts);

src/bin/pg_upgrade/task.c

@@ -188,6 +188,8 @@ start_conn(const ClusterInfo *cluster, UpgradeTaskSlot *slot)
 		appendPQExpBufferStr(&conn_opts, " host=");
 		appendConnStrVal(&conn_opts, cluster->sockdir);
 	}
+	if (!protocol_negotiation_supported(cluster))
+		appendPQExpBufferStr(&conn_opts, " max_protocol_version=3.0");
 
 	slot->conn = PQconnectStart(conn_opts.data);
 

src/bin/pg_upgrade/version.c

@@ -28,6 +28,24 @@ jsonb_9_4_check_applicable(ClusterInfo *cluster)
 	return false;
 }
 
+/*
+ * Older servers can't support newer protocol versions, so their connection
+ * strings will need to lock max_protocol_version to 3.0.
+ */
+bool
+protocol_negotiation_supported(const ClusterInfo *cluster)
+{
+	/*
+	 * The February 2018 patch release (9.3.21, 9.4.16, 9.5.11, 9.6.7, and
+	 * 10.2) added support for NegotiateProtocolVersion. But ClusterInfo only
+	 * has information about the major version number. To ensure we can still
+	 * upgrade older unpatched servers, just assume anything prior to PG11
+	 * can't negotiate. It's not possible for those servers to make use of
+	 * newer protocols anyway, so nothing is lost.
+	 */
+	return (GET_MAJOR_VERSION(cluster->major_version) >= 1100);
+}
+
 /*
  * old_9_6_invalidate_hash_indexes()
  *	9.6 -> 10