Remove nuke-room-from-db.sh script

[richvdh]

The problem with this script is that it is largely untested, entirely
unmaintained, and running it is likely to make your synapse blow up in
exciting ways.

For example, it leaves a bunch of tables with dead values in it, like
event_to_state_groups.

Having it here sends a message that it is a supported part of
synapse, which is absolutely not the case.

[jcgruenhage]

I probably would not have run this in the past, if I had known how unsupported it is. On the other hand, in the cases when I used it, it got my synapse back up and running after rooms got messed up somehow.

[hawkowl]

yes pls

[rubo77]

If i look at the database structure: #934

I think it is easy:

1. delete all entries in event_to_state_groups that match entries.entry_id with the key event_to_state_groups.entry_id

2. delete entries in event_to_state_groups

     SELECT * FROM event_to_state_groups s, events e WHERE s.event_id=e.event_id AND e.room_id like '%jGUBNvBzjGyQyKKMJV:matrix.org'
   

how do I delete only those entries now?

[richvdh]

none of that addresses the fact that we're not able to support and test it. I suggest you maintain your own sql script.

[rubo77]

I will :)

Delete data concerning only the room would be

 # (untested!) 
 DELETE 
    FROM event_to_state_groups USING events
    WHERE event_to_state_groups.event_id = events.event_id 
    AND room_id = '$ROOMID'

I think it is much easyer and also deletes orphaned entries like this:

DELETE FROM event_to_state_groups WHERE event_id NOT IN (SELECT event_id FROM events)

am I right?

@richvdh what other tables have orphaned entries after using the old nuke script?

[rubo77]

A more secure way to clear event_to_state_groups will be these commands:

-- check how many rows in event_to_state_groups

SELECT count(*) from event_to_state_groups;

-- create temporary TABLE event_to_state_groups_to_delete with event_ids that are missing in events TABLE

BEGIN;
SET enable_seqscan=off;
SELECT s.event_id INTO event_to_state_groups_to_delete FROM event_to_state_groups AS s 
LEFT JOIN events
ON s.event_id = events.event_id
WHERE events.event_id IS NULL;
COMMIT;

-- check how many rows will be deleted

SELECT count(*) from event_to_state_groups_to_delete;

(this can take some minutes if you have millions of events already)

shut synapse down to delete the entries

(not sure if shutdown is needed)

-- delete obsolete entries

DELETE FROM event_to_state_groups WHERE event_id IN (SELECT event_id FROM event_to_state_groups_to_delete);

start it up again

-- delete temporary TABLE event_to_state_groups_to_delete;

DROP TABLE event_to_state_groups_to_delete;

Do I understand it right, that event_to_state_groups only connects events with state_group on the same serer?
so If there are event_ids in event_to_state_groups that are not in events, they can be deleted?
And the same with the state_groups table: if there are event_ids in state_groups that are not in events, they can be deleted?

If so, then we would have to do the same deletion script with state_groups too?

[karl007]

For everyone who search for a secure solution to delete a room (or something nearby), I create a php script as replacement for the nuke-room-from-db script, but use the API to kick all users and then let the garbage collector remove the empty room instead of deleting membership in the DB (and maybe miss something or screw up the DB): https://gist.github.com/karl007/521f6ab84a398ee27118ab89aae7a9dc

php riot_delete_room.php https://matrix.org "MDA...kYK" "#alias:domain.de"

The script only shows all members and the stop and ask if the members should kick. Then ask for a reason and a possible userId which should not kicked.

[richvdh]

https://github.com/matrix-org/synapse/blob/master/docs/admin_api/purge_room.md

[rubo77]

The purge api seems to be only able to remove empty rooms.

The old nuke script was meant to repair unaccessible rooms, or rooms that contain errors. would the php script be able to remove those rooms too?

I would love to have a real new nuke-script (if the synapse api doesn't work any more for example to remove an old broken room with some foreign-key entries missing in my database that always sais, there is an unread message, but there isn't and where I cannot post or do anything inside any more)

[worldowner]

PHP script posted above won't delete private rooms if admin is not joined to them. What would be needed is an admin api that allows server admin to kick any user from any room regardless of membership. Then purge_room api could be used.

[rubo77]

/_synapse/admin/v1/purge_room can only purge rooms, that have no users in it, does this mean no users from your homeserver or no users at all?

It would be helpful to add an option to purge it also, if there are still users in it that didn't log in for some years

[worldowner]

purge_room will delete data if no local user (any user having account on homeserver that you call purge_api on) is a member of a room being purged.

It will delete data from your homeserver even if users of remote homeserver are still in this room. Data will obviously still persist on remote homeservers.

[rubo77]

So this will be a problem, if there is at least one user from your HS (that might not be active any more or even only logged in a few years ago and then forgot his password).