From 8e1ada9e6fdebe0cedaf39794a326196a9bd90d0 Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Wed, 17 Jul 2019 16:17:17 +0100
Subject: [PATCH] Use the current_state_events.membership column

---
 synapse/storage/roommember.py | 54 ++++++++++++++++++++++++-----------
 1 file changed, 37 insertions(+), 17 deletions(-)

diff --git a/synapse/storage/roommember.py b/synapse/storage/roommember.py
index f913abf8d..6541da3b8 100644
--- a/synapse/storage/roommember.py
+++ b/synapse/storage/roommember.py
@@ -115,14 +115,23 @@ class RoomMemberWorkerStore(EventsWorkerStore):
     @cached(max_entries=100000, iterable=True)
     def get_users_in_room(self, room_id):
         def f(txn):
-            sql = (
-                "SELECT m.user_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 = ? AND m.membership = ?"
-            )
+            # If we can assume current_state_events.membership is up to date
+            # then we can avoid a join, which is a Very Good Thing given how
+            # frequently this function gets called.
+            if self._current_state_events_membership_up_to_date:
+                sql = """
+                    SELECT state_key FROM current_state_events
+                    WHERE type = 'm.room.member' AND room_id = ? AND membership = ?
+                """
+            else:
+                sql = """
+                    SELECT state_key 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 = ? AND m.membership = ?
+                """
 
             txn.execute(sql, (room_id, Membership.JOIN))
             return [to_ascii(r[0]) for r in txn]
@@ -144,15 +153,26 @@ class RoomMemberWorkerStore(EventsWorkerStore):
             # first get counts.
             # We do this all in one transaction to keep the cache small.
             # FIXME: get rid of this when we have room_stats
-            sql = """
-                SELECT count(*), m.membership 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 = ?
-                 GROUP BY m.membership
-            """
+
+            # If we can assume current_state_events.membership is up to date
+            # then we can avoid a join, which is a Very Good Thing given how
+            # frequently this function gets called.
+            if self._current_state_events_membership_up_to_date:
+                sql = """
+                    SELECT count(*), membership FROM current_state_events
+                    WHERE type = 'm.room.member' AND room_id = ?
+                    GROUP BY membership
+                """
+            else:
+                sql = """
+                    SELECT count(*), m.membership 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 = ?
+                    GROUP BY m.membership
+                """
 
             txn.execute(sql, (room_id,))
             res = {}