Avoid rebuilding token metadata when topology has not changed

Author: thobbs

CHANGELOG.rst

@@ -19,6 +19,8 @@ Bug Fixes
 * Fix unintended rebuild of token replica map when keyspaces are
   discovered (on startup), added, or updated and TokenAwarePolicy is not
   in use.
+* Avoid rebuilding token metadata when cluster topology has not
+  actually changed
 
 1.1.2
 =====

cassandra/cluster.py

@@ -1629,6 +1629,7 @@ def _refresh_node_list_and_token_map(self, connection, preloaded_results=None):
             if partitioner and tokens:
                 token_map[host] = tokens
 
+        should_rebuild_token_map = False
         found_hosts = set()
         for row in peers_result:
             addr = row.get("rpc_address")
@@ -1645,8 +1646,9 @@ def _refresh_node_list_and_token_map(self, connection, preloaded_results=None):
             if host is None:
                 log.debug("[control connection] Found new host to connect to: %s", addr)
                 host = self._cluster.add_host(addr, datacenter, rack, signal=True)
+                should_rebuild_token_map = True
             else:
-                self._update_location_info(host, datacenter, rack)
+                should_rebuild_token_map |= self._update_location_info(host, datacenter, rack)
 
             tokens = row.get("tokens")
             if partitioner and tokens:
@@ -1657,22 +1659,25 @@ def _refresh_node_list_and_token_map(self, connection, preloaded_results=None):
                     old_host.address not in found_hosts and \
                     old_host.address not in self._cluster.contact_points:
                 log.debug("[control connection] Found host that has been removed: %r", old_host)
+                should_rebuild_token_map = True
                 self._cluster.remove_host(old_host)
 
-        if partitioner:
-            log.debug("[control connection] Fetched ring info, rebuilding metadata")
+        log.debug("[control connection] Finished fetching ring info")
+        if partitioner and should_rebuild_token_map:
+            log.debug("[control connection] Rebuilding token map due to topology changes")
             self._cluster.metadata.rebuild_token_map(partitioner, token_map)
 
     def _update_location_info(self, host, datacenter, rack):
         if host.datacenter == datacenter and host.rack == rack:
-            return
+            return False
 
         # If the dc/rack information changes, we need to update the load balancing policy.
         # For that, we remove and re-add the node against the policy. Not the most elegant, and assumes
         # that the policy will update correctly, but in practice this should work.
         self._cluster.load_balancing_policy.on_down(host)
         host.set_location_info(datacenter, rack)
         self._cluster.load_balancing_policy.on_up(host)
+        return True
 
     def _handle_topology_change(self, event):
         change_type = event["change_type"]