From 80467bbac3be6e008b807793dfd27c733936c15c Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Fri, 22 Feb 2019 14:38:14 +0000
Subject: [PATCH 1/2] Fix state cache invalidation on workers

---
 synapse/replication/slave/storage/_base.py |  7 +---
 synapse/storage/_base.py                   | 40 ++++++++++++++++++----
 2 files changed, 35 insertions(+), 12 deletions(-)

diff --git a/synapse/replication/slave/storage/_base.py b/synapse/replication/slave/storage/_base.py
index 1353a32d00..817d1f67f9 100644
--- a/synapse/replication/slave/storage/_base.py
+++ b/synapse/replication/slave/storage/_base.py
@@ -59,12 +59,7 @@ class BaseSlavedStore(SQLBaseStore):
                     members_changed = set(row.keys[1:])
                     self._invalidate_state_caches(room_id, members_changed)
                 else:
-                    try:
-                        getattr(self, row.cache_func).invalidate(tuple(row.keys))
-                    except AttributeError:
-                        # We probably haven't pulled in the cache in this worker,
-                        # which is fine.
-                        pass
+                    self._attempt_to_invalidate_cache(row.cache_func, tuple(row.keys))
 
     def _invalidate_cache_and_stream(self, txn, cache_func, keys):
         txn.call_after(cache_func.invalidate, keys)
diff --git a/synapse/storage/_base.py b/synapse/storage/_base.py
index 3d895da43c..5a80eef211 100644
--- a/synapse/storage/_base.py
+++ b/synapse/storage/_base.py
@@ -1342,15 +1342,43 @@ class SQLBaseStore(object):
                 changed
         """
         for member in members_changed:
-            self.get_rooms_for_user_with_stream_ordering.invalidate((member,))
+            self._attempt_to_invalidate_cache(
+                "get_rooms_for_user_with_stream_ordering", (member,),
+            )
 
         for host in set(get_domain_from_id(u) for u in members_changed):
-            self.is_host_joined.invalidate((room_id, host))
-            self.was_host_joined.invalidate((room_id, host))
+            self._attempt_to_invalidate_cache(
+                "is_host_joined", (room_id, host,),
+            )
+            self._attempt_to_invalidate_cache(
+                "was_host_joined", (room_id, host,),
+            )
 
-        self.get_users_in_room.invalidate((room_id,))
-        self.get_room_summary.invalidate((room_id,))
-        self.get_current_state_ids.invalidate((room_id,))
+        self._attempt_to_invalidate_cache(
+            "get_users_in_room", (room_id,),
+        )
+        self._attempt_to_invalidate_cache(
+            "get_room_summary", (room_id,),
+        )
+        self._attempt_to_invalidate_cache(
+            "get_current_state_ids", (room_id,),
+        )
+
+    def _attempt_to_invalidate_cache(self, cache_name, key):
+        """Attempts to invalidate the cache of the given name, ignoring if the
+        cache doesn't exist. Mainly used for invalidating caches on workers,
+        where they may not have the cache.
+
+        Args:
+            cache_name (str)
+            key (tuple)
+        """
+        try:
+            getattr(self, cache_name).invalidate(key)
+        except AttributeError:
+            # We probably haven't pulled in the cache in this worker,
+            # which is fine.
+            pass
 
     def _send_invalidation_to_replication(self, txn, cache_name, keys):
         """Notifies replication that given cache has been invalidated.

From e28ef831e6cac4f28012f2d3f3d8f09d813e40dc Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Fri, 22 Feb 2019 14:40:08 +0000
Subject: [PATCH 2/2] Newsfile

---
 changelog.d/4715.misc | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 changelog.d/4715.misc

diff --git a/changelog.d/4715.misc b/changelog.d/4715.misc
new file mode 100644
index 0000000000..4dc18378e7
--- /dev/null
+++ b/changelog.d/4715.misc
@@ -0,0 +1 @@
+Improve replication performance by reducing cache invalidation traffic.