Add forward extremities endpoint to rooms admin API

changelog.d/9062.feature

@@ -0,0 +1 @@
+Add admin API for getting and deleting forward extremities for a room.

docs/admin_api/rooms.md

@@ -9,6 +9,7 @@
  * [Response](#response)
  * [Undoing room shutdowns](#undoing-room-shutdowns)
 - [Make Room Admin API](#make-room-admin-api)
+- [Forward Extremities Admin API](#forward-extremities-admin-api)
 
 # List Room API
 
@@ -511,3 +512,55 @@ optionally be specified, e.g.:
  "user_id": "@foo:example.com"
  }
 ```
+
+# Forward Extremities Admin API
+
+Enables querying and deleting forward extremities from rooms. When a lot of forward
+extremities accumulate in a room, performance can become degraded. For details, see 
+[#1760](https://github.com/matrix-org/synapse/issues/1760).
+
+## Check for forward extremities
+
+To check the status of forward extremities for a room:
+
+```
+ GET /_synapse/admin/v1/rooms/<room_id_or_alias>/forward_extremities
+```
+
+A response as follows will be returned:
+
+```json
+{
+ "count": 1,
+ "results": [
+ {
+ "event_id": "$M5SP266vsnxctfwFgFLNceaCo3ujhRtg_NiiHabcdefgh",
+ "state_group": 439,
+ "depth": 123,
+ "received_ts": 1611263016761
+ }
+ ]
+} 
+```
+
+## Deleting forward extremities
+
+**WARNING**: Please ensure you know what you're doing and have read 
+the related issue [#1760](https://github.com/matrix-org/synapse/issues/1760).
+Under no situations should this API be executed as an automated maintenance task!
+
+If a room has lots of forward extremities, the extra can be
+deleted as follows:
+
+```
+ DELETE /_synapse/admin/v1/rooms/<room_id_or_alias>/forward_extremities
+```
+
+A response as follows will be returned, indicating the amount of forward extremities
+that were deleted.
+
+```json
+{
+ "deleted": 1
+}
+```

synapse/rest/admin/__init__.py

@@ -1,6 +1,8 @@
 # -*- coding: utf-8 -*-
 # Copyright 2014-2016 OpenMarket Ltd
 # Copyright 2018-2019 New Vector Ltd
+# Copyright 2020, 2021 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.
@@ -36,6 +38,7 @@
 from synapse.rest.admin.purge_room_servlet import PurgeRoomServlet
 from synapse.rest.admin.rooms import (
  DeleteRoomRestServlet,
+ ForwardExtremitiesRestServlet,
  JoinRoomAliasServlet,
  ListRoomRestServlet,
  MakeRoomAdminRestServlet,
@@ -230,6 +233,7 @@ def register_servlets(hs, http_server):
  EventReportsRestServlet(hs).register(http_server)
  PushersRestServlet(hs).register(http_server)
  MakeRoomAdminRestServlet(hs).register(http_server)
+ ForwardExtremitiesRestServlet(hs).register(http_server)
 
 
 def register_servlets_for_client_rest_resource(hs, http_server):

synapse/rest/admin/rooms.py

@@ -1,5 +1,5 @@
 # -*- coding: utf-8 -*-
-# Copyright 2019 The Matrix.org Foundation C.I.C.
+# Copyright 2019-2021 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.
@@ -499,3 +499,60 @@ async def on_POST(self, request, room_identifier):
  )
 
  return 200, {}
+
+
+class ForwardExtremitiesRestServlet(RestServlet):
+ """Allows a server admin to get or clear forward extremities.
+
+ Clearing does not require restarting the server.
+
+ Clear forward extremities:
+ DELETE /_synapse/admin/v1/rooms/<room_id_or_alias>/forward_extremities
+
+ Get forward_extremities:
+ GET /_synapse/admin/v1/rooms/<room_id_or_alias>/forward_extremities
+ """
+
+ PATTERNS = admin_patterns("/rooms/(?P<room_identifier>[^/]*)/forward_extremities")
+
+ def __init__(self, hs: "HomeServer"):
+ self.hs = hs
+ self.auth = hs.get_auth()
+ self.room_member_handler = hs.get_room_member_handler()
+ self.store = hs.get_datastore()
+
+ async def resolve_room_id(self, room_identifier: str) -> str:
+ """Resolve to a room ID, if necessary."""
+ if RoomID.is_valid(room_identifier):
+ resolved_room_id = room_identifier
+ elif RoomAlias.is_valid(room_identifier):
+ room_alias = RoomAlias.from_string(room_identifier)
+ room_id, _ = await self.room_member_handler.lookup_room_alias(room_alias)
+ resolved_room_id = room_id.to_string()
+ else:
+ raise SynapseError(
+ 400, "%s was not legal room ID or room alias" % (room_identifier,)
+ )
+ if not resolved_room_id:
+ raise SynapseError(
+ 400, "Unknown room ID or room alias %s" % room_identifier
+ )
+ return resolved_room_id
+
+ async def on_DELETE(self, request, room_identifier):
+ requester = await self.auth.get_user_by_req(request)
+ await assert_user_is_admin(self.auth, requester.user)
+
+ room_id = await self.resolve_room_id(room_identifier)
+
+ deleted_count = await self.store.delete_forward_extremities_for_room(room_id)
+ return 200, {"deleted": deleted_count}
+
+ async def on_GET(self, request, room_identifier):
+ requester = await self.auth.get_user_by_req(request)
+ await assert_user_is_admin(self.auth, requester.user)
+
+ room_id = await self.resolve_room_id(room_identifier)
+
+ extremities = await self.store.get_forward_extremities_for_room(room_id)
+ return 200, {"count": len(extremities), "results": extremities}

synapse/storage/databases/main/__init__.py

@@ -1,7 +1,7 @@
 # -*- coding: utf-8 -*-
 # Copyright 2014-2016 OpenMarket Ltd
 # Copyright 2018 New Vector Ltd
-# Copyright 2019 The Matrix.org Foundation C.I.C.
+# Copyright 2019-2021 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.
@@ -43,6 +43,7 @@
 from .event_federation import EventFederationStore
 from .event_push_actions import EventPushActionsStore
 from .events_bg_updates import EventsBackgroundUpdatesStore
+from .events_forward_extremities import EventForwardExtremitiesStore
 from .filtering import FilteringStore
 from .group_server import GroupServerStore
 from .keys import KeyStore
@@ -118,6 +119,7 @@ class DataStore(
  UIAuthStore,
  CacheInvalidationWorkerStore,
  ServerMetricsStore,
+ EventForwardExtremitiesStore,
 ):
  def __init__(self, database: DatabasePool, db_conn, hs):
  self.hs = hs

synapse/storage/databases/main/events_forward_extremities.py

@@ -0,0 +1,101 @@
+# -*- coding: utf-8 -*-
+# Copyright 2021 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.
+
+import logging
+from typing import Dict, List
+
+from synapse.api.errors import SynapseError
+from synapse.storage._base import SQLBaseStore
+
+logger = logging.getLogger(__name__)
+
+
+class EventForwardExtremitiesStore(SQLBaseStore):
+ async def delete_forward_extremities_for_room(self, room_id: str) -> int:
+ """Delete any extra forward extremities for a room.
+
+ Invalidates the "get_latest_event_ids_in_room" cache if any forward
+ extremities were deleted.
+
+ Returns count deleted.
+ """
+
+ def delete_forward_extremities_for_room_txn(txn):
+ # First we need to get the event_id to not delete
+ sql = """
+ SELECT event_id FROM event_forward_extremities
+ INNER JOIN events USING (room_id, event_id)
+ WHERE room_id = ?
+ ORDER BY stream_ordering DESC
+ LIMIT 1
+ """
+ txn.execute(sql, (room_id,))
+ rows = txn.fetchall()
+ try:
+ event_id = rows[0][0]
+ logger.debug(
+ "Found event_id %s as the forward extremity to keep for room %s",
+ event_id,
+ room_id,
+ )
+ except KeyError:
+ msg = "No forward extremity event found for room %s" % room_id
+ logger.warning(msg)
+ raise SynapseError(400, msg)
+
+ # Now delete the extra forward extremities
+ sql = """
+ DELETE FROM event_forward_extremities
+ WHERE event_id != ? AND room_id = ?
+ """
+
+ txn.execute(sql, (event_id, room_id))
+ logger.info(
+ "Deleted %s extra forward extremities for room %s",
+ txn.rowcount,
+ room_id,
+ )
+
+ if txn.rowcount > 0:
+ # Invalidate the cache
+ self._invalidate_cache_and_stream(
+ txn, self.get_latest_event_ids_in_room, (room_id,),
+ )
+
+ return txn.rowcount
+
+ return await self.db_pool.runInteraction(
+ "delete_forward_extremities_for_room",
+ delete_forward_extremities_for_room_txn,
+ )
+
+ async def get_forward_extremities_for_room(self, room_id: str) -> List[Dict]:
+ """Get list of forward extremities for a room."""
+
+ def get_forward_extremities_for_room_txn(txn):
+ sql = """
+ SELECT event_id, state_group, depth, received_ts
+ FROM event_forward_extremities
+ NATURAL JOIN event_to_state_groups
+ NATURAL JOIN events
+ WHERE room_id = ?
+ """
+
+ txn.execute(sql, (room_id,))
+ return self.db_pool.cursor_to_dict(txn)
+
+ return await self.db_pool.runInteraction(
+ "get_forward_extremities_for_room", get_forward_extremities_for_room_txn,
+ )