Servlet to purge old rooms (#5845)

changelog.d/5845.feature

+Add an admin API to purge old rooms from the database.

docs/admin_api/purge_room.md

+Purge room API
+==============
+
+This API will remove all trace of a room from your database.
+
+All local users must have left the room before it can be removed.
+
+The API is:
+
+```
+POST /_synapse/admin/v1/purge_room
+
+{
+    "room_id": "!room:id"
+}
+```
+
+You must authenticate using the access token of an admin user.

synapse/handlers/pagination.py

@@ -70,6 +70,7 @@ class PaginationHandler(object):
         self.auth = hs.get_auth()
         self.store = hs.get_datastore()
         self.clock = hs.get_clock()
+        self._server_name = hs.hostname
 
         self.pagination_lock = ReadWriteLock()
         self._purges_in_progress_by_room = set()
@@ -153,6 +154,22 @@ class PaginationHandler(object):
         """
         return self._purges_by_id.get(purge_id)
 
+    async def purge_room(self, room_id):
+        """Purge the given room from the database"""
+        with (await self.pagination_lock.write(room_id)):
+            # check we know about the room
+            await self.store.get_room_version(room_id)
+
+            # first check that we have no users in this room
+            joined = await defer.maybeDeferred(
+                self.store.is_host_joined, room_id, self._server_name
+            )
+
+            if joined:
+                raise SynapseError(400, "Users are still joined to this room")
+
+            await self.store.purge_room(room_id)
+
     @defer.inlineCallbacks
     def get_messages(
         self,

synapse/rest/admin/__init__.py

@@ -42,6 +42,7 @@ from synapse.rest.admin._base import (
     historical_admin_path_patterns,
 )
 from synapse.rest.admin.media import register_servlets_for_media_repo
+from synapse.rest.admin.purge_room_servlet import PurgeRoomServlet
 from synapse.rest.admin.server_notice_servlet import SendServerNoticeServlet
 from synapse.types import UserID, create_requester
 from synapse.util.versionstring import get_version_string
@@ -738,6 +739,7 @@ def register_servlets(hs, http_server):
     Register all the admin servlets.
     """
     register_servlets_for_client_rest_resource(hs, http_server)
+    PurgeRoomServlet(hs).register(http_server)
     SendServerNoticeServlet(hs).register(http_server)
     VersionServlet(hs).register(http_server)
 

synapse/rest/admin/purge_room_servlet.py

+# -*- coding: utf-8 -*-
+# Copyright 2019 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 re
+
+from synapse.http.servlet import (
+    RestServlet,
+    assert_params_in_dict,
+    parse_json_object_from_request,
+)
+from synapse.rest.admin import assert_requester_is_admin
+
+
+class PurgeRoomServlet(RestServlet):
+    """Servlet which will remove all trace of a room from the database
+
+    POST /_synapse/admin/v1/purge_room
+    {
+        "room_id": "!room:id"
+    }
+
+    returns:
+
+    {}
+    """
+
+    PATTERNS = (re.compile("^/_synapse/admin/v1/purge_room$"),)
+
+    def __init__(self, hs):
+        """
+        Args:
+            hs (synapse.server.HomeServer): server
+        """
+        self.hs = hs
+        self.auth = hs.get_auth()
+        self.pagination_handler = hs.get_pagination_handler()
+
+    async def on_POST(self, request):
+        await assert_requester_is_admin(self.auth, request)
+
+        body = parse_json_object_from_request(request)
+        assert_params_in_dict(body, ("room_id",))
+
+        await self.pagination_handler.purge_room(body["room_id"])
+
+        return (200, {})

synapse/storage/events.py

@@ -2181,6 +2181,143 @@ class EventsStore(
 
         return to_delete, to_dedelta
 
+    def purge_room(self, room_id):
+        """Deletes all record of a room
+
+        Args:
+            room_id (str):
+        """
+
+        return self.runInteraction("purge_room", self._purge_room_txn, room_id)
+
+    def _purge_room_txn(self, txn, room_id):
+        # first we have to delete the state groups states
+        logger.info("[purge] removing %s from state_groups_state", room_id)
+
+        txn.execute(
+            """
+            DELETE FROM state_groups_state WHERE state_group IN (
+              SELECT state_group FROM events JOIN event_to_state_groups USING(event_id)
+              WHERE events.room_id=?
+            )
+            """,
+            (room_id,),
+        )
+
+        # ... and the state group edges
+        logger.info("[purge] removing %s from state_group_edges", room_id)
+
+        txn.execute(
+            """
+            DELETE FROM state_group_edges WHERE state_group IN (
+              SELECT state_group FROM events JOIN event_to_state_groups USING(event_id)
+              WHERE events.room_id=?
+            )
+            """,
+            (room_id,),
+        )
+
+        # ... and the state groups
+        logger.info("[purge] removing %s from state_groups", room_id)
+
+        txn.execute(
+            """
+            DELETE FROM state_groups WHERE id IN (
+              SELECT state_group FROM events JOIN event_to_state_groups USING(event_id)
+              WHERE events.room_id=?
+            )
+            """,
+            (room_id,),
+        )
+
+        # and then tables which lack an index on room_id but have one on event_id
+        for table in (
+            "event_auth",
+            "event_edges",
+            "event_push_actions_staging",
+            "event_reference_hashes",
+            "event_relations",
+            "event_to_state_groups",
+            "redactions",
+            "rejections",
+            "state_events",
+        ):
+            logger.info("[purge] removing %s from %s", room_id, table)
+
+            txn.execute(
+                """
+                DELETE FROM %s WHERE event_id IN (
+                  SELECT event_id FROM events WHERE room_id=?
+                )
+                """
+                % (table,),
+                (room_id,),
+            )
+
+        # and finally, the tables with an index on room_id (or no useful index)
+        for table in (
+            "current_state_events",
+            "event_backward_extremities",
+            "event_forward_extremities",
+            "event_json",
+            "event_push_actions",
+            "event_search",
+            "events",
+            "group_rooms",
+            "public_room_list_stream",
+            "receipts_graph",
+            "receipts_linearized",
+            "room_aliases",
+            "room_depth",
+            "room_memberships",
+            "room_state",
+            "room_stats",
+            "room_stats_earliest_token",
+            "rooms",
+            "stream_ordering_to_exterm",
+            "topics",
+            "users_in_public_rooms",
+            "users_who_share_private_rooms",
+            # no useful index, but let's clear them anyway
+            "appservice_room_list",
+            "e2e_room_keys",
+            "event_push_summary",
+            "pusher_throttle",
+            "group_summary_rooms",
+            "local_invites",
+            "room_account_data",
+            "room_tags",
+        ):
+            logger.info("[purge] removing %s from %s", room_id, table)
+            txn.execute("DELETE FROM %s WHERE room_id=?" % (table,), (room_id,))
+
+        # Other tables we do NOT need to clear out:
+        #
+        #  - blocked_rooms
+        #    This is important, to make sure that we don't accidentally rejoin a blocked
+        #    room after it was purged
+        #
+        #  - user_directory
+        #    This has a room_id column, but it is unused
+        #
+
+        # Other tables that we might want to consider clearing out include:
+        #
+        #  - event_reports
+        #       Given that these are intended for abuse management my initial
+        #       inclination is to leave them in place.
+        #
+        #  - current_state_delta_stream
+        #  - ex_outlier_stream
+        #  - room_tags_revisions
+        #       The problem with these is that they are largeish and there is no room_id
+        #       index on them. In any case we should be clearing out 'stream' tables
+        #       periodically anyway (#5888)
+
+        # TODO: we could probably usefully do a bunch of cache invalidation here
+
+        logger.info("[purge] done")
+
     @defer.inlineCallbacks
     def is_event_after(self, event_id1, event_id2):
         """Returns True if event_id1 is after event_id2 in the stream