Reduce auth chains fetched during v2 state res. (#6952)

The state res v2 algorithm only cares about the difference between auth
chains, so we can pass in the known common state to the `get_auth_chain`
storage function so that it can ignore those events.

2 files changed, 11 insertions, 6 deletions

diff --git a/synapse/state/__init__.py b/synapse/state/__init__.py
index fdd6bef6b4..df7a4f6a89 100644
--- a/synapse/state/__init__.py
+++ b/synapse/state/__init__.py
@@ -16,7 +16,7 @@
 
 import logging
 from collections import namedtuple
-from typing import Dict, Iterable, List, Optional
+from typing import Dict, Iterable, List, Optional, Set
 
 from six import iteritems, itervalues
 
@@ -662,7 +662,7 @@ class StateResolutionStore(object):
             allow_rejected=allow_rejected,
         )
 
-    def get_auth_chain(self, event_ids):
+    def get_auth_chain(self, event_ids: List[str], ignore_events: Set[str]):
         """Gets the full auth chain for a set of events (including rejected
         events).
 
@@ -674,11 +674,16 @@ class StateResolutionStore(object):
                presence of rejected events
 
         Args:
-            event_ids (list): The event IDs of the events to fetch the auth
-                chain for. Must be state events.
+            event_ids: The event IDs of the events to fetch the auth chain for.
+                Must be state events.
+            ignore_events: Set of events to exclude from the returned auth
+                chain.
+
 
         Returns:
             Deferred[list[str]]: List of event IDs of the auth chain.
         """
 
-        return self.store.get_auth_chain_ids(event_ids, include_given=True)
+        return self.store.get_auth_chain_ids(
+            event_ids, include_given=True, ignore_events=ignore_events,
+        )
diff --git a/synapse/state/v2.py b/synapse/state/v2.py
index 531018c6a5..75fe58305a 100644
--- a/synapse/state/v2.py
+++ b/synapse/state/v2.py
@@ -248,7 +248,7 @@ def _get_auth_chain_difference(state_sets, event_map, state_res_store):
             and eid not in common
         )
 
-        auth_chain = yield state_res_store.get_auth_chain(auth_ids)
+        auth_chain = yield state_res_store.get_auth_chain(auth_ids, common)
         auth_ids.update(auth_chain)
 
         auth_sets.append(auth_ids)