From 0c4a99607e839c5a363351238a6a555015c8ddfc Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Wed, 24 Jul 2019 11:49:15 +0100
Subject: [PATCH] Remove join when calculating room summaries.

---
 synapse/storage/roommember.py | 34 +++++++++++++++++++++-------------
 1 file changed, 21 insertions(+), 13 deletions(-)

diff --git a/synapse/storage/roommember.py b/synapse/storage/roommember.py
index 7852d3866..bfb834ccc 100644
--- a/synapse/storage/roommember.py
+++ b/synapse/storage/roommember.py
@@ -179,19 +179,27 @@ class RoomMemberWorkerStore(EventsWorkerStore):
 
             # we order by membership and then fairly arbitrarily by event_id so
             # heroes are consistent
-            sql = """
-                SELECT m.user_id, m.membership, m.event_id
-                FROM room_memberships as m
-                 INNER JOIN current_state_events as c
-                 ON m.event_id = c.event_id
-                 AND m.room_id = c.room_id
-                 AND m.user_id = c.state_key
-                 WHERE c.type = 'm.room.member' AND c.room_id = ?
-                 ORDER BY
-                    CASE m.membership WHEN ? THEN 1 WHEN ? THEN 2 ELSE 3 END ASC,
-                    m.event_id ASC
-                 LIMIT ?
-            """
+            if self._current_state_events_membership_up_to_date:
+                sql = """
+                    SELECT state_key, membership, event_id
+                    FROM current_state_events
+                    WHERE type = 'm.room.member' AND room_id = ?
+                    ORDER BY
+                        CASE membership WHEN ? THEN 1 WHEN ? THEN 2 ELSE 3 END ASC,
+                        event_id ASC
+                    LIMIT ?
+                """
+            else:
+                sql = """
+                    SELECT c.state_key, m.membership, c.event_id
+                    FROM room_memberships as m
+                    INNER JOIN current_state_events as c USING (room_id, event_id)
+                    WHERE c.type = 'm.room.member' AND c.room_id = ?
+                    ORDER BY
+                        CASE m.membership WHEN ? THEN 1 WHEN ? THEN 2 ELSE 3 END ASC,
+                        c.event_id ASC
+                    LIMIT ?
+                """
 
             # 6 is 5 (number of heroes) plus 1, in case one of them is the calling user.
             txn.execute(sql, (room_id, Membership.JOIN, Membership.INVITE, 6))