policies: fix dc aware and rack aware policies initialization

dkropachev · dkropachev · commit b3c63c00faa0 · 2025-11-04T07:32:29.000-04:00
In cases when nodes are listed not in a proper groups of dc (for DCAwareRoundRobinPolicy) and dc+rack (for RackAwareRoundRobinPolicy).
Policy register only nodes from the last group or dc+rack.
So, policy knows only last group of nodes, rest of the nodes considered
to be non-existent, until node is restarted, which can be days.
diff --git a/cassandra/policies.py b/cassandra/policies.py
@@ -14,7 +14,6 @@
 import random
 
 from collections import namedtuple
-from functools import lru_cache
 from itertools import islice, cycle, groupby, repeat
 import logging
 from random import randint, shuffle
@@ -254,7 +253,7 @@ def _dc(self, host):
 
     def populate(self, cluster, hosts):
         for dc, dc_hosts in groupby(hosts, lambda h: self._dc(h)):
-            self._dc_live_hosts[dc] = tuple(set(dc_hosts))
+            self._dc_live_hosts[dc] = tuple({*dc_hosts, *self._dc_live_hosts.get(dc, [])})
 
         if not self.local_dc:
             self._endpoints = [
@@ -374,9 +373,9 @@ def _dc(self, host):
 
     def populate(self, cluster, hosts):
         for (dc, rack), rack_hosts in groupby(hosts, lambda host: (self._dc(host), self._rack(host))):
-            self._live_hosts[(dc, rack)] = tuple(set(rack_hosts))
+            self._live_hosts[(dc, rack)] = tuple({*rack_hosts, *self._live_hosts.get((dc, rack), [])})
         for dc, dc_hosts in groupby(hosts, lambda host: self._dc(host)):
-            self._dc_live_hosts[dc] = tuple(set(dc_hosts))
+            self._dc_live_hosts[dc] = tuple({*dc_hosts, *self._dc_live_hosts.get(dc, [])})
 
         self._position = randint(0, len(hosts) - 1) if hosts else 0
 
diff --git a/tests/unit/test_policies.py b/tests/unit/test_policies.py
@@ -11,7 +11,7 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-
+import random
 import unittest
 
 from itertools import islice, cycle
@@ -199,6 +199,8 @@ def test_no_remote(self, policy_specialization, constructor_args):
             h.set_location_info("dc1", "rack1")
             hosts.append(h)
 
+        random.shuffle(hosts)
+
         policy = policy_specialization(*constructor_args)
         policy.populate(None, hosts)
         qplan = list(policy.make_query_plan())
@@ -213,6 +215,8 @@ def test_with_remotes(self, policy_specialization, constructor_args):
         for h in hosts[4:]:
             h.set_location_info("dc2", "rack1")
 
+        random.shuffle(hosts)
+
         local_rack_hosts = set(h for h in hosts if h.datacenter == "dc1" and h.rack == "rack1")
         local_hosts = set(h for h in hosts if h.datacenter == "dc1" and h.rack != "rack1")
         remote_hosts = set(h for h in hosts if h.datacenter != "dc1")
