Fixup review comments

synapse/config/workers.py

@@ -94,13 +94,13 @@ class WorkerConfig(Config):
                     bind_addresses.append("")
 
         # A map from instance name to host/port of their HTTP replication endpoint.
-        instance_map = config.get("instance_map", {}) or {}
+        instance_map = config.get("instance_map") or {}
         self.instance_map = {
             name: InstanceLocationConfig(**c) for name, c in instance_map.items()
         }
 
         # Map from type of streams to source, c.f. WriterLocations.
-        writers = config.get("writers", {}) or {}
+        writers = config.get("writers") or {}
         self.writers = WriterLocations(**writers)
 
         # Check that the configured writer for events also appears in

synapse/handlers/message.py

@@ -888,7 +888,7 @@ class EventCreationHandler(object):
         """Called when we have fully built the event, have already
         calculated the push actions for the event, and checked auth.
 
-        This should only be run on master.
+        This should only be run on instance in charge of persisting events.
         """
         assert self.config.worker.writers.events == self._instance_name
 

synapse/replication/tcp/handler.py

@@ -89,6 +89,8 @@ class ReplicationCommandHandler:
                 self._streams_to_replicate.append(stream)
                 continue
 
+            # Only add EventStream and BackfillStream as a source on the
+            # instance in charge of event persistence.
             if (
                 isinstance(stream, (EventsStream, BackfillStream))
                 and hs.config.worker.writers.events == hs.get_instance_name()

synapse/storage/data_stores/__init__.py

@@ -67,7 +67,7 @@ class DataStores(object):
                     self.main = main_store_class(database, db_conn, hs)
 
                     # If we're on a process that can persist events also
-                    # instansiate a `PersistEventsStore`
+                    # instantiate a `PersistEventsStore`
                     if hs.config.worker.writers.events == hs.get_instance_name():
                         self.persist_events = PersistEventsStore(
                             hs, database, self.main