Track device list updates per room. (#12321)

This is a first step in dealing with #7721.

The idea is basically that rather than calculating the full set of users a device list update needs to be sent to up front, we instead simply record the rooms the user was in at the time of the change. This will allow a few things:

1. we can defer calculating the set of remote servers that need to be poked about the change; and
2. during `/sync` and `/keys/changes` we can avoid also avoid calculating users who share rooms with other users, and instead just look at the rooms that have changed.

However, care needs to be taken to correctly handle server downgrades. As such this PR writes to both `device_lists_changes_in_room` and the `device_lists_outbound_pokes` table synchronously. In a future release we can then bump the database schema compat version to `69` and then we can assume that the new `device_lists_changes_in_room` exists and is handled.

There is a temporary option to disable writing to `device_lists_outbound_pokes` synchronously, allowing us to test the new code path does work (and by implication upgrading to a future release and downgrading to this one will work correctly).

Note: Ideally we'd do the calculation of room to servers on a worker (e.g. the background worker), but currently only master can write to the `device_list_outbound_pokes` table.

2 files changed, 39 insertions, 0 deletions

diff --git a/synapse/storage/schema/__init__.py b/synapse/storage/schema/__init__.py
index ea900e0f3d..151f2aa9bb 100644
--- a/synapse/storage/schema/__init__.py
+++ b/synapse/storage/schema/__init__.py
@@ -60,6 +60,7 @@ Changes in SCHEMA_VERSION = 68:
       new events.
 
 Changes in SCHEMA_VERSION = 69:
+    - We now write to `device_lists_changes_in_room` table.
     - Use sequence to generate future `application_services_txns.txn_id`s
 """
 
diff --git a/synapse/storage/schema/main/delta/69/01device_list_oubound_by_room.sql b/synapse/storage/schema/main/delta/69/01device_list_oubound_by_room.sql
new file mode 100644
index 0000000000..b5b1782b2a
--- /dev/null
+++ b/synapse/storage/schema/main/delta/69/01device_list_oubound_by_room.sql
@@ -0,0 +1,38 @@
+/* Copyright 2022 The Matrix.org Foundation C.I.C
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+CREATE TABLE device_lists_changes_in_room (
+    user_id TEXT NOT NULL,
+    device_id TEXT NOT NULL,
+    room_id TEXT NOT NULL,
+
+    -- This initially matches `device_lists_stream.stream_id`. Note that we
+    -- delete older values from `device_lists_stream`, so we can't use a foreign
+    -- constraint here.
+    --
+    -- The table will contain rows with the same `stream_id` but different
+    -- `room_id`, as for each device update we store a row per room the user is
+    -- joined to. Therefore `(stream_id, room_id)` gives a unique index.
+    stream_id BIGINT NOT NULL,
+
+    -- We have a background process which goes through this table and converts
+    -- entries into rows in `device_lists_outbound_pokes`. Once we have processed
+    -- a row, we mark it as such by setting `converted_to_destinations=TRUE`.
+    converted_to_destinations BOOLEAN NOT NULL,
+    opentracing_context TEXT
+);
+
+CREATE UNIQUE INDEX device_lists_changes_in_stream_id ON device_lists_changes_in_room(stream_id, room_id);
+CREATE INDEX device_lists_changes_in_stream_id_unconverted ON device_lists_changes_in_room(stream_id) WHERE NOT converted_to_destinations;