Prefill events after invalidate not before when persisting events (#15758)

Fixes #15757

3 files changed, 20 insertions, 5 deletions

diff --git a/synapse/storage/databases/main/events.py b/synapse/storage/databases/main/events.py
index e2e6eb479f..44af3357af 100644
--- a/synapse/storage/databases/main/events.py
+++ b/synapse/storage/databases/main/events.py
@@ -1729,13 +1729,22 @@ class PersistEventsStore:
             if not row["rejects"] and not row["redacts"]:
                 to_prefill.append(EventCacheEntry(event=event, redacted_event=None))
 
-        async def prefill() -> None:
+        async def external_prefill() -> None:
             for cache_entry in to_prefill:
-                await self.store._get_event_cache.set(
+                await self.store._get_event_cache.set_external(
                     (cache_entry.event.event_id,), cache_entry
                 )
 
-        txn.async_call_after(prefill)
+        def local_prefill() -> None:
+            for cache_entry in to_prefill:
+                self.store._get_event_cache.set_local(
+                    (cache_entry.event.event_id,), cache_entry
+                )
+
+        # The order these are called here is not as important as knowing that after the
+        # transaction is finished, the async_call_after will run before the call_after.
+        txn.async_call_after(external_prefill)
+        txn.call_after(local_prefill)
 
     def _store_redaction(self, txn: LoggingTransaction, event: EventBase) -> None:
         assert event.redacts is not None
diff --git a/synapse/storage/databases/main/events_worker.py b/synapse/storage/databases/main/events_worker.py
index d93ffc4efa..7e7648c951 100644
--- a/synapse/storage/databases/main/events_worker.py
+++ b/synapse/storage/databases/main/events_worker.py
@@ -883,7 +883,7 @@ class EventsWorkerStore(SQLBaseStore):
 
     async def _invalidate_async_get_event_cache(self, event_id: str) -> None:
         """
-        Invalidates an event in the asyncronous get event cache, which may be remote.
+        Invalidates an event in the asynchronous get event cache, which may be remote.
 
         Arguments:
             event_id: the event ID to invalidate
diff --git a/synapse/util/caches/lrucache.py b/synapse/util/caches/lrucache.py
index 6137c85e10..be6554319a 100644
--- a/synapse/util/caches/lrucache.py
+++ b/synapse/util/caches/lrucache.py
@@ -842,7 +842,13 @@ class AsyncLruCache(Generic[KT, VT]):
         return self._lru_cache.get(key, update_metrics=update_metrics)
 
     async def set(self, key: KT, value: VT) -> None:
-        self._lru_cache.set(key, value)
+        # This will add the entries in the correct order, local first external second
+        self.set_local(key, value)
+        await self.set_external(key, value)
+
+    async def set_external(self, key: KT, value: VT) -> None:
+        # This method should add an entry to any configured external cache, in this case noop.
+        pass
 
     def set_local(self, key: KT, value: VT) -> None:
         self._lru_cache.set(key, value)