Use pg_rewind with --restore-target-wal on 13 if possible (#1525)

On PostgreSQL 13 check if restore_command is configured and tell pg_rewind to use it

patroni/postgresql/__init__.py

@@ -653,6 +653,15 @@ class Postgresql(object):
             return False
         return True
 
+    def get_guc_value(self, name):
+        cmd = [self.pgcommand('postgres'), self._data_dir, '-C', name]
+        try:
+            data = subprocess.check_output(cmd)
+            if data:
+                return data.decode('utf-8').strip()
+        except Exception as e:
+            logger.error('Failed to execute %s: %r', cmd, e)
+
     def controldata(self):
         """ return the contents of pg_controldata, or non-True value if pg_controldata call failed """
         # Don't try to call pg_controldata during backup restore

patroni/postgresql/rewind.py

@@ -173,9 +173,13 @@ class Rewind(object):
         env['PGOPTIONS'] = '-c statement_timeout=0'
         dsn = self._postgresql.config.format_dsn(r, True)
         logger.info('running pg_rewind from %s', dsn)
+
+        cmd = [self._postgresql.pgcommand('pg_rewind')]
+        if self._postgresql.major_version >= 130000 and self._postgresql.get_guc_value('restore_command'):
+            cmd.append('--restore-target-wal')
+        cmd.extend(['-D', self._postgresql.data_dir, '--source-server', dsn])
         try:
-            return self._postgresql.cancellable.call([self._postgresql.pgcommand('pg_rewind'), '-D',
-                                                      self._postgresql.data_dir, '--source-server', dsn], env=env) == 0
+            return self._postgresql.cancellable.call(cmd, env=env) == 0
         except OSError:
             return False
 

tests/test_rewind.py

@@ -35,13 +35,16 @@ class TestRewind(BaseTestPostgresql):
         self.p.config._config['use_pg_rewind'] = False
         self.assertFalse(self.r.can_rewind)
 
+    @patch.object(Postgresql, 'major_version', PropertyMock(return_value=130000))
     @patch.object(CancellableSubprocess, 'call')
     def test_pg_rewind(self, mock_cancellable_subprocess_call):
         r = {'user': '', 'host': '', 'port': '', 'database': '', 'password': ''}
         mock_cancellable_subprocess_call.return_value = 0
-        self.assertTrue(self.r.pg_rewind(r))
+        with patch('subprocess.check_output', Mock(return_value=b'foo')):
+            self.assertTrue(self.r.pg_rewind(r))
         mock_cancellable_subprocess_call.side_effect = OSError
-        self.assertFalse(self.r.pg_rewind(r))
+        with patch('subprocess.check_output', Mock(side_effect=Exception)):
+            self.assertFalse(self.r.pg_rewind(r))
 
     @patch.object(Rewind, 'can_rewind', PropertyMock(return_value=True))
     def test__get_local_timeline_lsn(self):