Make it possible to change use_slots online (#1261)

Previously it required restarting Patroni and removing slots manually
Fixes https://github.com/zalando/patroni/issues/1158

patroni/dcs/__init__.py

@@ -442,14 +442,16 @@ class Cluster(namedtuple('Cluster', 'initialize,config,leader,last_leader_operat
         # the current master, because that member would replicate from elsewhere. We still create the slot if
         # the replicatefrom destination member is currently not a member of the cluster (fallback to the
         # master), or if replicatefrom destination member happens to be the current master
+        use_slots = self.config and self.config.data.get('postgresql', {}).get('use_slots', True)
         if role in ('master', 'standby_leader'):
-            slot_members = [m.name for m in self.members if m.name != name and
+            slot_members = [m.name for m in self.members if use_slots and m.name != name and
                             (m.replicatefrom is None or m.replicatefrom == name or
                              not self.has_member(m.replicatefrom))]
             permanent_slots = (self.config and self.config.permanent_slots or {}).copy()
         else:
             # only manage slots for replicas that replicate from this one, except for the leader among them
-            slot_members = [m.name for m in self.members if m.replicatefrom == name and m.name != self.leader.name]
+            slot_members = [m.name for m in self.members if use_slots and
+                            m.replicatefrom == name and m.name != self.leader.name]
             permanent_slots = {}
 
         slots = {slot_name_from_member_name(name): {'type': 'physical'} for name in slot_members}

patroni/postgresql/config.py

@@ -502,7 +502,8 @@ class ConfigHandler(object):
         primary_conninfo = self.primary_conninfo_params(member)
         if primary_conninfo:
             recovery_params['primary_conninfo'] = primary_conninfo
-            if self._postgresql.slots_handler.use_slots and not (is_remote_master and member.no_replication_slot):
+            if self.get('use_slots', True) and self._postgresql.major_version >= 90400 \
+                    and not (is_remote_master and member.no_replication_slot):
                 recovery_params['primary_slot_name'] = member.primary_slot_name if is_remote_master \
                         else slot_name_from_member_name(self._postgresql.name)
 

patroni/postgresql/slots.py

@@ -15,19 +15,14 @@ class SlotsHandler(object):
 
     def __init__(self, postgresql):
         self._postgresql = postgresql
-        self._use_slots = postgresql.config.get('use_slots', True)
         self._replication_slots = {}  # already existing replication slots
         self.schedule()
 
-    @property
-    def use_slots(self):
-        return self._use_slots and self._postgresql.major_version >= 90400
-
     def _query(self, sql, *params):
         return self._postgresql.query(sql, *params, retry=False)
 
     def load_replication_slots(self):
-        if self.use_slots and self._schedule_load_slots:
+        if self._postgresql.major_version >= 90400 and self._schedule_load_slots:
             replication_slots = {}
             cursor = self._query('SELECT slot_name, slot_type, plugin, database FROM pg_catalog.pg_replication_slots')
             for r in cursor:
@@ -45,7 +40,7 @@ class SlotsHandler(object):
         return cursor.rowcount == 1
 
     def sync_replication_slots(self, cluster):
-        if self.use_slots:
+        if self._postgresql.major_version >= 90400:
             try:
                 self.load_replication_slots()
 
@@ -104,5 +99,5 @@ class SlotsHandler(object):
 
     def schedule(self, value=None):
         if value is None:
-            value = self.use_slots
+            value = self._postgresql.major_version >= 90400
         self._schedule_load_slots = value