state resets still happen in v2 rooms

[matrixbot]

This issue has been migrated from #8629.

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I just upgraded #synapse:matrix.org because I got fed up of losing my ops bit. It was a v4 room.

EDIT 2022-08-03 by @DMRobertson: if you suspect you have seen a state reset, please provide:

• the room_id of the room with the reset
• the type and state_key that suffered a reset
• the event_id of the piece of state after the reset
• ideally, the event_id of the piece of state before the reset
  • failing that, a rough time range before and after the reset occurred (including timezone information)

To confirm if this really is a server-side state reset (rather than e.g. matrix-org/matrix-spec#1209), server administrators can run the following queries.

SELECT *
FROM current_state_delta_stream 
WHERE
	room_id ='<room id>'
	and type='<type of event>'' 
    and state_key='<state key>'
ORDER BY stream_id asc;

SELECT *
FROM current_state_events
WHERE
	room_id ='<room id>'
	and type='<type of event>'' 
    and state_key='<state key>';

The last row in the event_id columns from these two queries should match. It represents the event which currently describes the relevant piece of state from your server's point of view.

[Mikaela]

Continuing from matrix-org/synapse#8629, could someone take a look at #furrytech:matrix.org (room ID !furrytechv10:jae.fi as GitHub still doesn't support Matrix URI scheme)?

We don't have willing homeserver admins available, but pikaviestin.fi (Synapse) is unable to see at least the-apothecary.club (Synapse), xmr.se (Synapse?) and 777.tf (Dendrite) and every homeserver seems to see different set of users there, which I understand to be a case of this issue.