Timeline navigation misbehaving starting from 10000 posts

[Canapin (Coin-coin le Canapin)]

Hi.
I noticed after an import that the timeline navigation don’t work properly on 10000+ posts topics.
If you drag’n drop the cursor on the timeline, it will scroll to the post, but won’t update the timeline cursor until you scroll again manually:

My max reply limits is the default one: 10000. So it shouldn’t be an issue…
Except that Discourse closes a message at the post number 10000, and add another reply (automatic closure), which makes 10001 posts.

But even at 10000 replies, the issue occurs.
However, the issue disappears as soon as delete posts to have 9999 replies (including the automatic closure message):

So, the issue occurs naturally when the topic reaches 10000 replies, and not only for existing megatopics.

I increased the auto close topics post count setting but it didn’t resolve the issue.
I also tried to change the short progress text threshold and it didn’t help either. Weirdly, even by increasing this setting to 15000, the timeline cursor doesn’t show the date on a 10000 posts thread

But that may be another issue.

[Falco]

@Canapin

If you drag’n drop the cursor on the timeline, it will scroll to the post, but won’t update the timeline cursor until you scroll again manually:

This is because

@tgxworld

Jumping to an index on the timeline becomes jumping to the closest post number on the timeline

@Canapin

Weirdly, even by increasing this setting to 15000, the timeline cursor doesn’t show the date on a 10000 posts thread

We remove a lot of features on mega topics to preserve performance. Our general recommendation is The MEGATOPIC: public good, or public menace?

@codinghorror

Yes, server load gets exponentially higher with large topics. We put in some basic mitigations (you’ll note that dates don’t appear on the timeline, etc) but it’s still expensive.

@sam

The number of megatopics in the wild is minuscule, investing large amount of time optimising this means we have less time working on features which are much more commonly needed.

[Canapin (Coin-coin le Canapin)]

Thank you for your reply
I’ve read these post and I understand why megatopics are wrong.

The main “problem” to me is just that the issue course naturally with default Discourse settings, and wouldn’t occur if the limit was 9998 instead of 10000. But I acknowledge that this is a rare issue and a very minor inconvenience.