Some messages appear out of order

[vthriller]

Description

Some messages appear out of order, like on this screenshot from #mozilla_#servo:matrix.org:

The following are the snippets of said messages sources:

{
  "origin_server_ts": 1526498974801,
  "sender": "@mozilla_crowbot:matrix.org",
  …
  "age": 503879905,
  "unsigned": {
    "age": 503879905
  },
  …
}

{
  "origin_server_ts": 1526498969477,
  "sender": "@mozilla_jdm:matrix.org",
  …
  "age": 503885229,
  "unsigned": {
    "age": 503885229
  },
  …
}

And, obviously,

>>> 1526498974801 > 1526498969477
True
>>> 503879905 < 503885229
True

Steps to reproduce

• Join something.
• Accumulate a week or so of unread conversations.
• Read all the messages.
• Try again if failed to reproduce.

I'm able to replicate this by just looking for 20472, or 20632, or uluru/pull/8 in #mozilla_#servo:matrix.org's history (which, unfortunately, is not available for those who just joined the room).

Log: not sent

Version information

• Platform: web
• Browser: Firefox 57
• OS: Gentoo Linux
• URL: riot.im/app (0.15.2 at the time of writing this issue)

[t3chguy]

This could be caused by network delays and/or two servers disagreeing on the exact time. Its impossible to order by time in the server because that means you're trusting the time, and I could easily send an event from 1970 if I wanted to and you'd inject it to before the room even existed if you trusted me, its a common tradeoff in a publicly federated system

[lampholder]

As I understand it this is, as @t3chguy says, an unavoidable tradeoff and so I'm afraid not something that is going to be changed.

[ghost]

Good day,

We are seeing some messages appear out of order between the riot iOS app and the riot web client.

We are hosting our own synapse home server (0.99.5.1+stretch1) on Debian 9. We also host our own riot web client (v1.1.2).

The browser used to access the web client is firefox-esr (60.7.0esr-1~deb9u1), also running on Debian 9.

Our home server is configured not to federate (both in configuration and firewall settings). We only have a single home server, so there is no chance of two home servers disagreeing.

This seems to be a bug.

[turt2live]

1.1.2 has a bug which should be fixed in 1.2.0 (due to be released soon - there is a RC available).

I'm actually going to close this issue as there's nothing actionable on it.