Detect unknown remote devices and mark cache as stale (#6776)

We just mark the fact that the cache may be stale in the database for
now.

synapse/storage/data_stores/main/devices.py

@@ -457,7 +457,7 @@ class DeviceWorkerStore(SQLBaseStore):
                 device = yield self._get_cached_user_device(user_id, device_id)
                 results.setdefault(user_id, {})[device_id] = device
             else:
-                results[user_id] = yield self._get_cached_devices_for_user(user_id)
+                results[user_id] = yield self.get_cached_devices_for_user(user_id)
 
         set_tag("in_cache", results)
         set_tag("not_in_cache", user_ids_not_in_cache)
@@ -475,12 +475,12 @@ class DeviceWorkerStore(SQLBaseStore):
         return db_to_json(content)
 
     @cachedInlineCallbacks()
-    def _get_cached_devices_for_user(self, user_id):
+    def get_cached_devices_for_user(self, user_id):
         devices = yield self.db.simple_select_list(
             table="device_lists_remote_cache",
             keyvalues={"user_id": user_id},
             retcols=("device_id", "content"),
-            desc="_get_cached_devices_for_user",
+            desc="get_cached_devices_for_user",
         )
         return {
             device["device_id"]: db_to_json(device["content"]) for device in devices
@@ -641,6 +641,18 @@ class DeviceWorkerStore(SQLBaseStore):
 
         return results
 
+    def mark_remote_user_device_cache_as_stale(self, user_id: str):
+        """Records that the server has reason to believe the cache of the devices
+        for the remote users is out of date.
+        """
+        return self.db.simple_upsert(
+            table="device_lists_remote_resync",
+            keyvalues={"user_id": user_id},
+            values={},
+            insertion_values={"added_ts": self._clock.time_msec()},
+            desc="make_remote_user_device_cache_as_stale",
+        )
+
 
 class DeviceBackgroundUpdateStore(SQLBaseStore):
     def __init__(self, database: Database, db_conn, hs):
@@ -887,7 +899,7 @@ class DeviceStore(DeviceWorkerStore, DeviceBackgroundUpdateStore):
             )
 
         txn.call_after(self._get_cached_user_device.invalidate, (user_id, device_id))
-        txn.call_after(self._get_cached_devices_for_user.invalidate, (user_id,))
+        txn.call_after(self.get_cached_devices_for_user.invalidate, (user_id,))
         txn.call_after(
             self.get_device_list_last_stream_id_for_remote.invalidate, (user_id,)
         )
@@ -902,6 +914,13 @@ class DeviceStore(DeviceWorkerStore, DeviceBackgroundUpdateStore):
             lock=False,
         )
 
+        # If we're replacing the remote user's device list cache presumably
+        # we've done a full resync, so we remove the entry that says we need
+        # to resync
+        self.db.simple_delete_txn(
+            txn, table="device_lists_remote_resync", keyvalues={"user_id": user_id},
+        )
+
     def update_remote_device_list_cache(self, user_id, devices, stream_id):
         """Replace the entire cache of the remote user's devices.
 
@@ -942,7 +961,7 @@ class DeviceStore(DeviceWorkerStore, DeviceBackgroundUpdateStore):
             ],
         )
 
-        txn.call_after(self._get_cached_devices_for_user.invalidate, (user_id,))
+        txn.call_after(self.get_cached_devices_for_user.invalidate, (user_id,))
         txn.call_after(self._get_cached_user_device.invalidate_many, (user_id,))
         txn.call_after(
             self.get_device_list_last_stream_id_for_remote.invalidate, (user_id,)

synapse/storage/data_stores/main/schema/delta/57/device_list_remote_cache_stale.sql

@@ -0,0 +1,25 @@
+/* Copyright 2020 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.
+ */
+
+-- Records whether the server thinks that the remote users cached device lists
+-- may be out of date (e.g. if we have received a to device message from a
+-- device we don't know about).
+CREATE TABLE IF NOT EXISTS device_lists_remote_resync (
+    user_id TEXT NOT NULL,
+    added_ts BIGINT NOT NULL
+);
+
+CREATE UNIQUE INDEX device_lists_remote_resync_idx ON device_lists_remote_resync (user_id);
+CREATE INDEX device_lists_remote_resync_ts_idx ON device_lists_remote_resync (added_ts);