Review comments

synapse/storage/__init__.py

@@ -29,7 +29,7 @@ stored in `synapse.storage.schema`.
 
 from synapse.storage.data_stores import DataStores
 from synapse.storage.data_stores.main import DataStore
-from synapse.storage.persist_events import EventsPersistenceStore
+from synapse.storage.persist_events import EventsPersistenceStorage
 
 __all__ = ["DataStores", "DataStore"]
 
@@ -44,7 +44,7 @@ class Storage(object):
         # interfaces.
         self.main = stores.main
 
-        self.persistence = EventsPersistenceStore(hs, stores)
+        self.persistence = EventsPersistenceStorage(hs, stores)
 
 
 def are_all_users_on_domain(txn, database_engine, domain):

synapse/storage/data_stores/main/events.py

@@ -146,7 +146,7 @@ class EventsStore(
 
     @_retry_on_integrity_error
     @defer.inlineCallbacks
-    def _persist_events(
+    def _persist_events_and_state_updates(
         self,
         events_and_contexts,
         current_state_for_room,
@@ -155,18 +155,27 @@ class EventsStore(
         backfilled=False,
         delete_existing=False,
     ):
-        """Persist events to db
+        """Persist a set of events alongside updates to the current state and
+        forward extremities tables.
 
         Args:
             events_and_contexts (list[(EventBase, EventContext)]):
-            backfilled (bool):
+            current_state_for_room (dict[str, dict]): Map from room_id to the
+                current state of the room based on forward extremities
+            state_delta_for_room (dict[str, tuple]): Map from room_id to tuple
+                of `(to_delete, to_insert)` where to_delete is a list
+                of type/state keys to remove from current state, and to_insert
+                is a map (type,key)->event_id giving the state delta in each
+                room.
+            new_forward_extremities (dict[str, list[str]]): Map from room_id
+                to list of event IDs that are the new forward extremities of
+                the room.
+            backfilled (bool)
             delete_existing (bool):
 
         Returns:
             Deferred: resolves when the events have been persisted
         """
-        if not events_and_contexts:
-            return
 
         # We want to calculate the stream orderings as late as possible, as
         # we only notify after all events with a lesser stream ordering have

synapse/storage/persist_events.py

@@ -171,7 +171,13 @@ class _EventPeristenceQueue(object):
             pass
 
 
-class EventsPersistenceStore(object):
+class EventsPersistenceStorage(object):
+    """High level interface for handling persisting newly received events.
+
+    Takes care of batching up events by room, and calculating the necessary
+    current state and forward extremity changes.
+    """
+
     def __init__(self, hs, stores: DataStores):
         # We ultimately want to split out the state store from the main store,
         # so we use separate variables here even though they point to the same
@@ -257,7 +263,8 @@ class EventsPersistenceStore(object):
     def _persist_events(
         self, events_and_contexts, backfilled=False, delete_existing=False
     ):
-        """Persist events to db
+        """Calculates the change to current state and forward extremities, and
+        persists the given events and with those updates.
 
         Args:
             events_and_contexts (list[(EventBase, EventContext)]):
@@ -399,7 +406,7 @@ class EventsPersistenceStore(object):
                         if current_state is not None:
                             current_state_for_room[room_id] = current_state
 
-            yield self.main_store._persist_events(
+            yield self.main_store._persist_events_and_state_updates(
                 chunk,
                 current_state_for_room=current_state_for_room,
                 state_delta_for_room=state_delta_for_room,