From 3a0b44c7a86a4bfae96aa5fc1e6f045c2d838a18 Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Wed, 10 Jul 2024 14:57:26 +0100
Subject: Faster room sorting

---
 synapse/handlers/sliding_sync.py         | 34 ++++----------------------------
 synapse/storage/databases/main/stream.py | 25 ++++++++++++++++++++++-
 2 files changed, 28 insertions(+), 31 deletions(-)

diff --git a/synapse/handlers/sliding_sync.py b/synapse/handlers/sliding_sync.py
index 818b13621c..0d4d764483 100644
--- a/synapse/handlers/sliding_sync.py
+++ b/synapse/handlers/sliding_sync.py
@@ -1006,36 +1006,10 @@ class SlidingSyncHandler:
             A sorted list of room IDs by `stream_ordering` along with membership information.
         """
 
-        # Assemble a map of room ID to the `stream_ordering` of the last activity that the
-        # user should see in the room (<= `to_token`)
-        last_activity_in_room_map: Dict[str, int] = {}
-        for room_id, room_for_user in sync_room_map.items():
-            # If they are fully-joined to the room, let's find the latest activity
-            # at/before the `to_token`.
-            if room_for_user.membership == Membership.JOIN:
-                last_event_result = (
-                    await self.store.get_last_event_pos_in_room_before_stream_ordering(
-                        room_id, to_token.room_key
-                    )
-                )
-
-                # If the room has no events at/before the `to_token`, this is probably a
-                # mistake in the code that generates the `sync_room_map` since that should
-                # only give us rooms that the user had membership in during the token range.
-                assert last_event_result is not None
-
-                _, event_pos = last_event_result
-
-                last_activity_in_room_map[room_id] = event_pos.stream
-            else:
-                # Otherwise, if the user has left/been invited/knocked/been banned from
-                # a room, they shouldn't see anything past that point.
-                #
-                # FIXME: It's possible that people should see beyond this point in
-                # invited/knocked cases if for example the room has
-                # `invite`/`world_readable` history visibility, see
-                # https://github.com/matrix-org/matrix-spec-proposals/pull/3575#discussion_r1653045932
-                last_activity_in_room_map[room_id] = room_for_user.event_pos.stream
+        # XXX: FIXUP
+        last_activity_in_room_map = await self.store.rough_get_last_pos(
+            sync_room_map.keys()
+        )
 
         return sorted(
             sync_room_map.values(),
diff --git a/synapse/storage/databases/main/stream.py b/synapse/storage/databases/main/stream.py
index e74e0d2e91..dccae56608 100644
--- a/synapse/storage/databases/main/stream.py
+++ b/synapse/storage/databases/main/stream.py
@@ -78,7 +78,7 @@ from synapse.storage.database import (
 from synapse.storage.databases.main.events_worker import EventsWorkerStore
 from synapse.storage.engines import BaseDatabaseEngine, PostgresEngine, Sqlite3Engine
 from synapse.storage.util.id_generators import MultiWriterIdGenerator
-from synapse.types import PersistedEventPosition, RoomStreamToken
+from synapse.types import PersistedEventPosition, RoomStreamToken, StrSequence
 from synapse.util.caches.descriptors import cached
 from synapse.util.caches.stream_change_cache import StreamChangeCache
 from synapse.util.cancellation import cancellable
@@ -1185,6 +1185,29 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore):
 
         return None
 
+
+    async def rough_get_last_pos(self, room_ids: StrSequence) -> Dict[str, int]:
+        def rough_get_last_pos_Txn(
+            txn: LoggingTransaction,
+        ) -> Dict[str, int]:
+            clause, args = make_in_list_sql_clause(self.database_engine, "room_id", room_ids)
+            sql = f"""
+                SELECT room_id, MAX(stream_ordering) FROM events
+                WHERE {clause}
+                GROUP BY room_id
+            """
+
+            txn.execute(sql, (args,))
+
+            return {
+                room_id: stream_ordering for room_id, stream_ordering in txn
+            }
+
+        return await self.db_pool.runInteraction(
+            "rough_get_last_pos",
+            rough_get_last_pos_Txn,
+        )
+
     async def get_last_event_pos_in_room_before_stream_ordering(
         self,
         room_id: str,
-- 
cgit 1.4.1