Make pagination of rooms in admin api stable (#11737)

Always add state.room_id after the configurable ORDER BY. Otherwise,
for any sort, certain pages can contain results from
other pages. (Especially when sorting by creator, since there may
be many rooms by the same creator)

* Document different order direction of numerical fields

"joined_members", "joined_local_members", "version" and "state_events"
are ordered in descending direction by default (dir=f). Added a note
in tests to explain the differences in ordering.

Signed-off-by: Daniël Sonck <daniel@sonck.nl>

3 files changed, 38 insertions, 28 deletions

diff --git a/changelog.d/11737.bugfix b/changelog.d/11737.bugfix
new file mode 100644

index 0000000000..a293d1cfec
--- /dev/null
+++ b/changelog.d/11737.bugfix
@@ -0,0 +1 @@
+Make the list rooms admin api sort stable. Contributed by Daniël Sonck.
\ No newline at end of file
diff --git a/synapse/storage/databases/main/room.py b/synapse/storage/databases/main/room.py

index c0e837854a..95167116c9 100644
--- a/synapse/storage/databases/main/room.py
+++ b/synapse/storage/databases/main/room.py
@@ -551,24 +551,24 @@ class RoomWorkerStore(CacheInvalidationWorkerStore):
             FROM room_stats_state state
             INNER JOIN room_stats_current curr USING (room_id)
             INNER JOIN rooms USING (room_id)
-            %s
-            ORDER BY %s %s
+            {where}
+            ORDER BY {order_by} {direction}, state.room_id {direction}
             LIMIT ?
             OFFSET ?
-        """ % (
-            where_statement,
-            order_by_column,
-            "ASC" if order_by_asc else "DESC",
+        """.format(
+            where=where_statement,
+            order_by=order_by_column,
+            direction="ASC" if order_by_asc else "DESC",
         )
 
         # Use a nested SELECT statement as SQL can't count(*) with an OFFSET
         count_sql = """
             SELECT count(*) FROM (
               SELECT room_id FROM room_stats_state state
-              %s
+              {where}
             ) AS get_room_ids
-        """ % (
-            where_statement,
+        """.format(
+            where=where_statement,
         )
 
         def _get_rooms_paginate_txn(
diff --git a/tests/rest/admin/test_room.py b/tests/rest/admin/test_room.py

index d2c8781cd4..3495a0366a 100644
--- a/tests/rest/admin/test_room.py
+++ b/tests/rest/admin/test_room.py
@@ -1089,6 +1089,8 @@ class RoomTestCase(unittest.HomeserverTestCase):
             )
             room_ids.append(room_id)
 
+        room_ids.sort()
+
         # Request the list of rooms
         url = "/_synapse/admin/v1/rooms"
         channel = self.make_request(
@@ -1360,6 +1362,12 @@ class RoomTestCase(unittest.HomeserverTestCase):
         room_id_2 = self.helper.create_room_as(self.admin_user, tok=self.admin_user_tok)
         room_id_3 = self.helper.create_room_as(self.admin_user, tok=self.admin_user_tok)
 
+        # Also create a list sorted by IDs for properties that are equal (and thus sorted by room_id)
+        sorted_by_room_id_asc = [room_id_1, room_id_2, room_id_3]
+        sorted_by_room_id_asc.sort()
+        sorted_by_room_id_desc = sorted_by_room_id_asc.copy()
+        sorted_by_room_id_desc.reverse()
+
         # Set room names in alphabetical order. room 1 -> A, 2 -> B, 3 -> C
         self.helper.send_state(
             room_id_1,
@@ -1405,41 +1413,42 @@ class RoomTestCase(unittest.HomeserverTestCase):
         _order_test("canonical_alias", [room_id_1, room_id_2, room_id_3])
         _order_test("canonical_alias", [room_id_3, room_id_2, room_id_1], reverse=True)
 
+        # Note: joined_member counts are sorted in descending order when dir=f
         _order_test("joined_members", [room_id_3, room_id_2, room_id_1])
         _order_test("joined_members", [room_id_1, room_id_2, room_id_3], reverse=True)
 
+        # Note: joined_local_member counts are sorted in descending order when dir=f
         _order_test("joined_local_members", [room_id_3, room_id_2, room_id_1])
         _order_test(
             "joined_local_members", [room_id_1, room_id_2, room_id_3], reverse=True
         )
 
-        _order_test("version", [room_id_1, room_id_2, room_id_3])
-        _order_test("version", [room_id_1, room_id_2, room_id_3], reverse=True)
+        # Note: versions are sorted in descending order when dir=f
+        _order_test("version", sorted_by_room_id_asc, reverse=True)
+        _order_test("version", sorted_by_room_id_desc)
 
-        _order_test("creator", [room_id_1, room_id_2, room_id_3])
-        _order_test("creator", [room_id_1, room_id_2, room_id_3], reverse=True)
+        _order_test("creator", sorted_by_room_id_asc)
+        _order_test("creator", sorted_by_room_id_desc, reverse=True)
 
-        _order_test("encryption", [room_id_1, room_id_2, room_id_3])
-        _order_test("encryption", [room_id_1, room_id_2, room_id_3], reverse=True)
+        _order_test("encryption", sorted_by_room_id_asc)
+        _order_test("encryption", sorted_by_room_id_desc, reverse=True)
 
-        _order_test("federatable", [room_id_1, room_id_2, room_id_3])
-        _order_test("federatable", [room_id_1, room_id_2, room_id_3], reverse=True)
+        _order_test("federatable", sorted_by_room_id_asc)
+        _order_test("federatable", sorted_by_room_id_desc, reverse=True)
 
-        _order_test("public", [room_id_1, room_id_2, room_id_3])
-        # Different sort order of SQlite and PostreSQL
-        # _order_test("public", [room_id_3, room_id_2, room_id_1], reverse=True)
+        _order_test("public", sorted_by_room_id_asc)
+        _order_test("public", sorted_by_room_id_desc, reverse=True)
 
-        _order_test("join_rules", [room_id_1, room_id_2, room_id_3])
-        _order_test("join_rules", [room_id_1, room_id_2, room_id_3], reverse=True)
+        _order_test("join_rules", sorted_by_room_id_asc)
+        _order_test("join_rules", sorted_by_room_id_desc, reverse=True)
 
-        _order_test("guest_access", [room_id_1, room_id_2, room_id_3])
-        _order_test("guest_access", [room_id_1, room_id_2, room_id_3], reverse=True)
+        _order_test("guest_access", sorted_by_room_id_asc)
+        _order_test("guest_access", sorted_by_room_id_desc, reverse=True)
 
-        _order_test("history_visibility", [room_id_1, room_id_2, room_id_3])
-        _order_test(
-            "history_visibility", [room_id_1, room_id_2, room_id_3], reverse=True
-        )
+        _order_test("history_visibility", sorted_by_room_id_asc)
+        _order_test("history_visibility", sorted_by_room_id_desc, reverse=True)
 
+        # Note: state_event counts are sorted in descending order when dir=f
         _order_test("state_events", [room_id_3, room_id_2, room_id_1])
         _order_test("state_events", [room_id_1, room_id_2, room_id_3], reverse=True)