Don't needlessly batch in add_event_to_cache

changelog.d/10784.misc

@@ -0,0 +1 @@
+Minor speed ups when joining large rooms over federation.

synapse/storage/databases/main/events.py

@@ -1547,35 +1547,32 @@ def _add_to_cache(self, txn, events_and_contexts):
         to_prefill = []
 
         rows = []
-        N = 200
-        for i in range(0, len(events_and_contexts), N):
-            ev_map = {e[0].event_id: e[0] for e in events_and_contexts[i : i + N]}
-            if not ev_map:
-                break
-
-            sql = (
-                "SELECT "
-                " e.event_id as event_id, "
-                " r.redacts as redacts,"
-                " rej.event_id as rejects "
-                " FROM events as e"
-                " LEFT JOIN rejections as rej USING (event_id)"
-                " LEFT JOIN redactions as r ON e.event_id = r.redacts"
-                " WHERE "
-            )
 
-            clause, args = make_in_list_sql_clause(
-                self.database_engine, "e.event_id", list(ev_map)
-            )
+        ev_map = {e.event_id: e for e, _ in events_and_contexts}
+        if not ev_map:
+            return
 
-            txn.execute(sql + clause, args)
-            rows = self.db_pool.cursor_to_dict(txn)
-            for row in rows:
-                event = ev_map[row["event_id"]]
-                if not row["rejects"] and not row["redacts"]:
-                    to_prefill.append(
-                        _EventCacheEntry(event=event, redacted_event=None)
-                    )
+        sql = (
+            "SELECT "
+            " e.event_id as event_id, "
+            " r.redacts as redacts,"
+            " rej.event_id as rejects "
+            " FROM events as e"
+            " LEFT JOIN rejections as rej USING (event_id)"
+            " LEFT JOIN redactions as r ON e.event_id = r.redacts"
+            " WHERE "
+        )
+
+        clause, args = make_in_list_sql_clause(
+            self.database_engine, "e.event_id", list(ev_map)
+        )
+
+        txn.execute(sql + clause, args)
+        rows = self.db_pool.cursor_to_dict(txn)
+        for row in rows:
+            event = ev_map[row["event_id"]]
+            if not row["rejects"] and not row["redacts"]:
+                to_prefill.append(_EventCacheEntry(event=event, redacted_event=None))
 
         def prefill():
             for cache_entry in to_prefill: