File redactions not immediately propagated

[Akselmo]

Description

I was in a channel which is owned by another homeserver where someone posted bad things. Those bad things were then deleted.

However, the redaction event was not propagated over the federation for over 30 minutes. I am not sure if it still is there, but I am not unblocking the user who sent those messages.

This left multiple users having to see the harmful content.

Steps to reproduce

• Synapse server A.org hosts a channel
• user user:B.org joins a channel
• user:B.org posts an image
• admin:A.org deletes the image/message and bans the account
• Synapse server user random:C.org still sees the redacted messages/images even after 30 minutes

Homeserver

mx.scalie.zone is my homeserver, kde.org is the channel owner, maintained by EMS

Synapse Version

1.116.0, the channel owning homeserver is on 1.115.0 i think

Installation Method

Debian packages from packages.matrix.org

Database

PostgreSQL, single server, no ports

Workers

Single process

Platform

My homeserver uses this: https://www.netcup.com/en/server/vps/vps-1000-g11-12m-iv

Configuration

No response

Relevant log output

Unsure if exactly relevant, but I saw warnings like this where the spammer account is mentioned.

2024-10-03 12:05:42,416 - synapse.handlers.federation_event - 2044 - WARNING - _process_incoming_pdus_in_room_inner-44011-$0Pkscx0uwpmvoVymcgckLzUAhGG0zJlVBVm7KWU9EFs - Soft-failing <FrozenEventV3 event_id=$0Pkscx0uwpmvoVymcgckLzUAhGG0zJlVBVm7KWU9EFs, type=m.room.message, state_key=None, outlier=False> (from 403: User @SPAMMER:SPAMMER_SERVER not in room !gYaaEyvNWxTzXssOmq:kde.org (<FrozenEventV3 event_id=$Gv_JvV4vwnGLV008f6rXFHrJZWtdu0TCKxHx7TBAjdg, type=m.room.member, state_key=@SPAMMER:SPAMMER_SERVER, outlier=False>)) because SPAMMER_SERVER

It just ends there, theres no more after "because SPAMMER_SERVER"

and yes the username is a placeholder there

### Anything else that would be useful to know?

_No response_

[daedric7]

You've got this whole "channel owner" thing wrong.

There are no channels, there are rooms.

Rooms do not belong or exist in one server. All servers in the federation have a copy of said room. Matrix is full-mesh, all servers participating in that room federation must send all events to each and every other server.

Now, let's take this fact into your pratical example:

mx.scalie.zone is my homeserver, kde.org is the channel owner, maintained by EMS

Your server, and kde.org is inside said room. Someone, probably NOT from kde.org or your server, sent bad media. Then, someone, maybe from kde.org, maybe not, redacted that message.

This redaction must reach your homeserver for you to see. If your homeserver cannot comunicate with the server from the user sending the redaction, it will take much longer for your server, and for you, to see that redaction (you must get it from another server via backfill)

[Akselmo]

There are no channels, there are rooms.

Fine, whatever you call it. You know what I meant anyway.

This redaction must reach your homeserver for you to see. If your homeserver cannot comunicate with the server from the user sending the redaction, it will take much longer for your server, and for you, to see that redaction (you must get it from another server via backfill)

What steps can I/we take for this to not happen? What is weird about this is that I saw normal messages just fine, but the deletion didn't happen at all. The users of any homeserver, even the owner of the room, could send a message and I saw them immediately. I was even told that the harmful media was already deleted, yet it wasn't for me.

If I can see messages from admin/moderator of that room, but not the file redactions, why?