Order of events after a federation outage is confusing

[chagai95]

Steps to reproduce

1. The server was down for a few hours.

Outcome

What did you expect?

Eventual consistency

What happened instead?

The timeline showing on one server is not the same as the other server.

Operating system

Windows

Browser information

Version 93.0.4577.63 (Official Build) (64-bit)

URL for webapp

https://app.element.io, chat.chagai.website

Application version

Element version: 1.9.5 Olm version: 3.2.3, Element Chagai version: v1.8.5 Olm version: 3.2.3

Homeserver

matrix.org, chagai.website

Will you send logs?

Yes

[t3chguy]

The timeline content & order is provided by the server. During server outages, old messages may come down /sync as new ones and the client has no way to tell them apart.

[chagai95]

So if I understood correctly it's a server issue, closing it here

[chagai95]

Unsure if there's enough information or not for the clients to mark them reliably and consistently — would need a client dev's perspective on whether we ought to think about a clearer way to tell clients about this case (which would need protocol changes/specification work).

matrix-org/synapse#11499 (comment)

@t3chguy @reivilibre not sure where you prefer to discuss this but it seems like the server devs think the client devs might have enough info and the client devs think they don't.

[MadLittleMods]

Related to:

• Very old events appear out of order in the live timeline after federation backfill element-meta#1491
• Messages can appear out of order if /sync is delayed but message PUTs are 200ing element-meta#1934
• Vector should display consistent ordering on timelines. element-meta#1900

[MadLittleMods]

Closing in favor of element-hq/element-meta#1491