Fix a few little issues with 9.5 support (#3260)

1. pg_rewind error log format wasn't verbose
2. it doesn't support specifying num in synchronous_standby_names

patroni/postgresql/rewind.py

@@ -135,9 +135,10 @@ class Rewind(object):
                 # Message format depends on the major version:
                 # * expected at least -- starting from v16
                 # * wanted -- before v16
+                # * nothing (end of message) 9.5 and older
                 # We will simply check all possible combinations.
-                for pattern in (': expected at least ', ': wanted '):
-                    j = err[0].find(pattern, i)
+                for pattern in (': expected at least ', ': wanted ', '\n'):
+                    j = (err[0] + '\n').find(pattern, i)
                     if j > -1:
                         try:
                             return parse_lsn(err[0][i:j])

patroni/postgresql/sync.py

@@ -408,7 +408,7 @@ END;$$""")
         else:
             sync_param = next(iter(sync), None)
 
-        if global_config.is_quorum_commit_mode and sync or self._postgresql.supports_multiple_sync and len(sync) > 1:
+        if self._postgresql.supports_multiple_sync and (global_config.is_quorum_commit_mode and sync or len(sync) > 1):
             prefix = 'ANY ' if global_config.is_quorum_commit_mode and self._postgresql.supports_quorum_commit else ''
             sync_param = f'{prefix}{num} ({sync_param})'
 

tests/test_rewind.py

@@ -194,6 +194,14 @@ class TestRewind(BaseTestPostgresql):
             self.r.trigger_check_diverged_lsn()
             self.assertFalse(self.r.rewind_or_reinitialize_needed_and_possible(self.leader))
 
+            mock_popen.return_value.communicate.return_value = (
+                b'0, lsn: 0/040159C1, prev 0/\n',
+                b'pg_waldump: fatal: error in WAL record at 0/40159C1: invalid record length at 0/402DD98\n'
+            )
+            self.r.reset_state()
+            self.r.trigger_check_diverged_lsn()
+            self.assertFalse(self.r.rewind_or_reinitialize_needed_and_possible(self.leader))
+
             self.r.reset_state()
             self.r.trigger_check_diverged_lsn()
             mock_popen.side_effect = Exception

tests/test_sync.py

@@ -155,6 +155,17 @@ class TestSync(BaseTestPostgresql):
         mock_reload.assert_called()
         self.assertEqual(value_in_conf(), "synchronous_standby_names = '3 (a,b)'")
 
+        self.p._major_version = 90501
+        mock_reload.reset_mock()
+        self.s.set_synchronous_standby_names([], 1)
+        mock_reload.assert_called()
+        self.assertEqual(value_in_conf(), "synchronous_standby_names = '*'")
+
+        mock_reload.reset_mock()
+        self.s.set_synchronous_standby_names(['a-1'], 1)
+        mock_reload.assert_called()
+        self.assertEqual(value_in_conf(), "synchronous_standby_names = '\"a-1\"'")
+
     @patch.object(Postgresql, 'last_operation', Mock(return_value=1))
     def test_do_not_prick_yourself(self):
         self.p.name = self.leadermem.name