Remove restrictions on running pg_rewind.

Previously, pg_rewind was called only if a crashed master tried
to rejoin the cluster. It didn't cover the important case of a
master shut down cleanly, but with a combination of a smart
shutdown and subsequently a fast shutdown. Since out pg_rewind
code does not depend on the "uncleanness" of the master's shutdown,
we can call it unconditionally in all cases where the former master
tries to rejoin as a replica.

This resolves  #167.

patroni/ha.py

@@ -106,12 +106,6 @@ class Ha(object):
             return 'waiting for leader to bootstrap'
 
     def recover(self):
-        # try to see if we are the former master that crashed. If so - we likely need to run pg_rewind
-        # in order to join the former standby being promoted.
-        if self.state_handler.role == 'master':
-            pg_controldata = self.state_handler.controldata()
-            if pg_controldata and pg_controldata.get('Database cluster state', '') == 'in production':  # crashed master
-                self.state_handler.require_rewind()
         self.recovering = True
         return self.follow("starting as readonly because i had the session lock", "starting as a secondary", True, True)
 

patroni/postgresql.py

@@ -73,7 +73,6 @@ class Postgresql(object):
 
         self._connection = None
         self._cursor_holder = None
-        self._need_rewind = False
         self._sysid = None
         self.replication_slots = []  # list of already existing replication slots
         self.retry = Retry(max_tries=-1, deadline=5, max_delay=1, retry_exceptions=PostgresConnectionException)
@@ -115,9 +114,6 @@ class Postgresql(object):
             self._sysid = data.get('Database system identifier', "")
         return self._sysid
 
-    def require_rewind(self):
-        self._need_rewind = True
-
     def get_local_address(self):
         listen_addresses = self.listen_addresses.split(',')
         local_address = listen_addresses[0].strip()  # take first address from listen_addresses
@@ -564,13 +560,12 @@ recovery_target_timeline = 'latest'
     def follow(self, leader, recovery=False):
         if self.check_recovery_conf(leader) and not recovery:
             return True
-
         change_role = self.role == 'master'
-        self._need_rewind = (self._need_rewind or change_role) and self.can_rewind
-        if self._need_rewind:
+        need_rewind = change_role and self.can_rewind
+        if need_rewind:
             logger.info("set the rewind flag after demote")
         self.write_recovery_conf(leader)
-        if leader and self._need_rewind:  # we have a leader and need to rewind
+        if leader and need_rewind:  # we have a leader and need to rewind
             if self.is_running():
                 self.stop()
             # at present, pg_rewind only runs when the cluster is shut down cleanly
@@ -594,7 +589,6 @@ recovery_target_timeline = 'latest'
                 logger.error("unable to rewind the former master")
                 self.remove_data_directory()
                 ret = True
-            self._need_rewind = False
         else:  # do not rewind until the leader becomes available
             ret = self.restart()
         if change_role and ret:
@@ -630,7 +624,6 @@ recovery_target_timeline = 'latest'
         if ret:
             self.set_role('master')
             logger.info("cleared rewind flag after becoming the leader")
-            self._need_rewind = False
             self.call_nowait(ACTION_ON_ROLE_CHANGE)
         return ret
 

tests/test_postgresql.py

@@ -257,12 +257,10 @@ class TestPostgresql(unittest.TestCase):
         self.p.follow(Leader(-1, 28, self.other))
         self.p.rewind = mock_pg_rewind
         self.p.follow(self.leader)
-        self.p.require_rewind()
         with mock.patch('os.path.islink', MagicMock(return_value=True)):
             with mock.patch('patroni.postgresql.Postgresql.can_rewind', new_callable=PropertyMock(return_value=True)):
                 with mock.patch('os.unlink', MagicMock(return_value=True)):
                     self.p.follow(self.leader, recovery=True)
-        self.p.require_rewind()
         with mock.patch('patroni.postgresql.Postgresql.can_rewind', new_callable=PropertyMock(return_value=True)):
             self.p.rewind.return_value = True
             self.p.follow(self.leader, recovery=True)