From c77dae7a1abfef19940efd1378df5e2215a5b48b Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Tue, 23 Feb 2016 14:48:23 +0000
Subject: [PATCH] Change the way we figure out presence updates for small
 deltas

---
 synapse/handlers/presence.py               | 53 +++++++++++++++-------
 synapse/util/caches/stream_change_cache.py | 16 +++++++
 2 files changed, 52 insertions(+), 17 deletions(-)

diff --git a/synapse/handlers/presence.py b/synapse/handlers/presence.py
index 80de4f43b6..84624d4902 100644
--- a/synapse/handlers/presence.py
+++ b/synapse/handlers/presence.py
@@ -845,35 +845,54 @@ class PresenceEventSource(object):
             room_ids = room_ids or []
 
             presence = self.hs.get_handlers().presence_handler
+            stream_change_cache = self.store.presence_stream_cache
 
             if not room_ids:
                 rooms = yield self.store.get_rooms_for_user(user_id)
                 room_ids = set(e.room_id for e in rooms)
-
-            user_ids_to_check = set()
-            for room_id in room_ids:
-                users = yield self.store.get_users_in_room(room_id)
-                user_ids_to_check.update(users)
+            else:
+                room_ids = set(room_ids)
 
             plist = yield self.store.get_presence_list_accepted(user.localpart)
-            user_ids_to_check.update([row["observed_user_id"] for row in plist])
+            friends = set(row["observed_user_id"] for row in plist)
+            friends.add(user_id)  # So that we receive our own presence
 
-            # Always include yourself. Only really matters for when the user is
-            # not in any rooms, but still.
-            user_ids_to_check.add(user_id)
+            user_ids_changed = set()
+            if from_key and from_key < 100:
+                changed = stream_change_cache.get_all_entities_changed(from_key)
 
-            max_token = self.store.get_current_presence_token()
-
-            if from_key:
-                user_ids_changed = self.store.presence_stream_cache.get_entities_changed(
-                    user_ids_to_check, from_key,
-                )
+                for other_user_id in changed:
+                    if other_user_id in friends:
+                        user_ids_changed.add(other_user_id)
+                        continue
+                    other_rooms = yield self.store.get_rooms_for_user(other_user_id)
+                    if room_ids.intersection(e.room_id for e in other_rooms):
+                        user_ids_changed.add(other_user_id)
+                        continue
             else:
-                user_ids_changed = user_ids_to_check
+                user_ids_to_check = set()
+                for room_id in room_ids:
+                    users = yield self.store.get_users_in_room(room_id)
+                    user_ids_to_check.update(users)
+
+                plist = yield self.store.get_presence_list_accepted(user.localpart)
+                user_ids_to_check.update([row["observed_user_id"] for row in plist])
+
+                # Always include yourself. Only really matters for when the user is
+                # not in any rooms, but still.
+                user_ids_to_check.add(user_id)
+
+                if from_key:
+                    user_ids_changed = stream_change_cache.get_entities_changed(
+                        user_ids_to_check, from_key,
+                    )
+                else:
+                    user_ids_changed = user_ids_to_check
 
             updates = yield presence.current_state_for_users(user_ids_changed)
 
-            now = self.clock.time_msec()
+        max_token = self.store.get_current_presence_token()
+        now = self.clock.time_msec()
 
         defer.returnValue(([
             {
diff --git a/synapse/util/caches/stream_change_cache.py b/synapse/util/caches/stream_change_cache.py
index b37f1c0725..970488a19c 100644
--- a/synapse/util/caches/stream_change_cache.py
+++ b/synapse/util/caches/stream_change_cache.py
@@ -85,6 +85,22 @@ class StreamChangeCache(object):
 
         return result
 
+    def get_all_entities_changed(self, stream_pos):
+        """Returns all entites that have had new things since the given
+        position. If the position is too old it will return None.
+        """
+        assert type(stream_pos) is int
+
+        if stream_pos >= self._earliest_known_stream_pos:
+            keys = self._cache.keys()
+            i = keys.bisect_right(stream_pos)
+
+            return (
+                self._cache[k] for k in keys[i:]
+            )
+        else:
+            return None
+
     def entity_has_changed(self, entity, stream_pos):
         """Informs the cache that the entity has been changed at the given
         position.