One thing we’ve noticed come up on a few sites is a pattern of behavior where
users make almost no public posts, but spend most of their time in very, very long PM topics that can be tens of thousands of replies long
There are a few problems with this:
We currently have a massive perf problem with longer topics as we send down a list of all IDs of all replies in the topic, which can be enormous – if the topic is 50k replies long, it includes 50k ids in a list in every request. Longer term we do plan to fix this, but restricting very long topics is something we need to do in the short term, unless there is a very good reason for a topic to have 50k replies, it should be avoided.
Private reply activity is fine, in context with other public activity, but when almost all your activity is private, it feels a bit counter to the goals of the overall community and is certainly not something we want to encourage.
We totally get that some communities want a chat feature very badly, and this is something that is solidly on our medium term roadmap. We hear you loud and clear and we largely agree; there’s a legitimate need for a more real time “lane” on the highway. But abusing Discourse personal messages to force it into a private chat system is not the right way to support that feature.
It skews activity data on the site, so the public side of the site which is what most see will be unusually slow despite “good post volume”, while there is this giant burgeoning secret clique-ish underground that few have visibility into.
Thus, we’ve decided to add a new site setting for maximum allowed replies in a PM topic and it will default to 200. After that limit is hit, the PM will be auto-closed by the system user with a brief explanation and reminder something like
This personal message was automatically closed after reaching the maximum of 200 replies. Consider adopting a chat system if you need long term, persistent personal messaging.
This should introduce some desired friction into this behavior, making it harder to abuse, without unreasonably limiting “real” personal message topics.