Purge History API is not deleting all messages

[nabil-ak]

Description

Hello,
Do anyone know why the Purge History Endpoint in the Admin API is not clearing the whole chat? The documentation says that there has to be one message left in the room but when I try to clean the chat there is always a few messages left that he dosen't want to delete...

Steps to reproduce

1. Made a Post request to this endpoint
   curl --location '....../_synapse/admin/v1/purge_history/<roomid>' \ --header 'accept: application/json' \ --header 'authorization: Bearer...' \ --header 'Content-Type: application/json' \ --data '{ "delete_local_events": true, "purge_up_to_ts": 1683112888849 }'

2. Not all messages got deleted there are still 2-4 messages left

Homeserver

privat homeserver

Synapse Version

1.78.0

Installation Method

Docker (matrixdotorg/synapse)

Database

PostgreSQL

Workers

Single process

Platform

running in a docker container

Configuration

No response

Relevant log output

no logs

Anything else that would be useful to know?

No response

[squahtx]

Please note that the docs say that there will be at least one message remaining in the room afterward.

The remaining messages are expected to be the forward extremities of the room DAG, that is, messages which have not yet been cited as prev_events by any future messages. Multiple forward extremities are likely to occur in federated rooms when different homservers send events around the same time.