Refactor `EventContext` (#12689)

Refactor how the `EventContext` class works, with the intention of reducing the amount of state we fetch from the DB during event processing.

The idea here is to get rid of the cached `current_state_ids` and `prev_state_ids` that live in the `EventContext`, and instead defer straight to the database (and its caching). 

One change that may have a noticeable effect is that we now no longer prefill the `get_current_state_ids` cache on a state change. However, that query is relatively light, since its just a case of reading a table from the DB (unlike fetching state at an event which is more heavyweight). For deployments with workers this cache isn't even used.


Part of #12684

1 files changed, 0 insertions, 6 deletions

diff --git a/synapse/storage/databases/main/events.py b/synapse/storage/databases/main/events.py
index 6c12653bb3..f544bcfff0 100644
--- a/synapse/storage/databases/main/events.py
+++ b/synapse/storage/databases/main/events.py
@@ -128,7 +128,6 @@ class PersistEventsStore:
         self,
         events_and_contexts: List[Tuple[EventBase, EventContext]],
         *,
-        current_state_for_room: Dict[str, StateMap[str]],
         state_delta_for_room: Dict[str, DeltaState],
         new_forward_extremities: Dict[str, Set[str]],
         use_negative_stream_ordering: bool = False,
@@ -139,8 +138,6 @@ class PersistEventsStore:
 
         Args:
             events_and_contexts:
-            current_state_for_room: Map from room_id to the current state of
-                the room based on forward extremities
             state_delta_for_room: Map from room_id to the delta to apply to
                 room state
             new_forward_extremities: Map from room_id to set of event IDs
@@ -215,9 +212,6 @@ class PersistEventsStore:
 
                 event_counter.labels(event.type, origin_type, origin_entity).inc()
 
-            for room_id, new_state in current_state_for_room.items():
-                self.store.get_current_state_ids.prefill((room_id,), new_state)
-
             for room_id, latest_event_ids in new_forward_extremities.items():
                 self.store.get_latest_event_ids_in_room.prefill(
                     (room_id,), list(latest_event_ids)