better logging if _handle_slots (#52)

src/main.py

@@ -1175,15 +1175,21 @@ def _handle_slots(self):
 
         # create slots
         slot_names = [helpers.app_name_from_fqdn(fqdn) for fqdn in slot_lock_holders]
+        actual_replication_slots = self.db.get_replication_slots()
+        if actual_replication_slots is None:
+            logging.warning('Failed to get actual replication slots')
+            # However, we can continue here and try to create slots. None of slots will be dropped, but some might be created
+        else:
+            logging.debug('Actual replication slots: %s', actual_replication_slots)
 
-        if not self.db.replication_slots('create', slot_names):
+        if not self.db.create_replication_slots(slot_names, verbose=False):
             logging.warning('Could not create replication slots. %s', slot_names)
 
         # drop slots
         if my_hostname in non_holders_hosts:
             non_holders_hosts.remove(my_hostname)
         slot_names_to_drop = [helpers.app_name_from_fqdn(fqdn) for fqdn in non_holders_hosts]
-        if not self.db.replication_slots('drop', slot_names_to_drop):
+        if not self.db.drop_replication_slots(slot_names_to_drop, verbose=False):
             logging.warning('Could not drop replication slots. %s', slot_names_to_drop)
 
     def _get_db_state(self):
@@ -1350,7 +1356,7 @@ def _promote_handle_slots(self):
                 return False
             # Create replication slots, regardless of whether replicas hold DCS locks for replication slots.
             hosts = [helpers.app_name_from_fqdn(fqdn) for fqdn in hosts]
-            if not self.db.replication_slots('create', hosts):
+            if not self.db.create_replication_slots(hosts):
                 logging.error('Could not create replication slots. Releasing the lock in ZK.')
                 return False
 

src/pg.py

@@ -143,15 +143,17 @@ def _offline_detect_pgdata(self):
                 logging.error(line.rstrip())
 
     @helpers.return_none_on_error
-    def _get_replication_slots(self):
+    def get_replication_slots(self):
         res = self._exec_query('SELECT slot_name FROM pg_replication_slots;').fetchall()
         return [i[0] for i in res]
 
     def _create_replication_slot(self, slot_name):
+        logging.info('Creating slot %s.', slot_name)
         query = f"SELECT pg_create_physical_replication_slot('{slot_name}', true)"
         return self._exec_without_result(query)
 
     def _drop_replication_slot(self, slot_name):
+        logging.info('Dropping slot %s.', slot_name)
         query = f"SELECT pg_drop_replication_slot('{slot_name}')"
         return self._exec_without_result(query)
 
@@ -736,24 +738,26 @@ def stop_postgresql(self, timeout=60):
                 logging.warning(line.rstrip())
         return self._cmd_manager.stop_postgresql(timeout, self.pgdata)
 
-    def replication_slots(self, action, slots):
-        """
-        Perform replication slots action (create/drop)
-        """
-        current = self._get_replication_slots()
+    def create_replication_slots(self, slots, verbose=True):
+        current = self.get_replication_slots()
         for slot in slots:
-            if action == 'create':
-                if current and slot in current:
+            if current and slot in current:
+                if verbose:
                     logging.debug('Slot %s already exists.', slot)
-                    continue
-                if not self._create_replication_slot(slot):
-                    return False
-            else:
-                if current is not None and slot not in current:
+                continue
+            if not self._create_replication_slot(slot):
+                return False
+        return True
+
+    def drop_replication_slots(self, slots, verbose=True):
+        current = self.get_replication_slots()
+        for slot in slots:
+            if current is not None and slot not in current:
+                if verbose:
                     logging.debug('Slot %s does not exist.', slot)
-                    continue
-                if not self._drop_replication_slot(slot):
-                    return False
+                continue
+            if not self._drop_replication_slot(slot):
+                return False
         return True
 
     def is_replaying_wal(self, check_time):