No Stupid Questions @lemmy.world dohpaz42 @lemmy.world 9 mo. ago

Why does Lemmy (and reddit) show posts from previous page on next page?

When scrolling through Lemmy, I often will see the same posts from the previous page - usually as the first links on the current page I'm on.

19 comments

Just speculating but, as new posts are made, it pushes the other posts up some, which can make them show up again when you hit next (or hit the infinite scrolling reload point).
Lazy programming.

The naive way to do pagination is to say show me items x through y. But obviously if the back end is dynamic, x through y could change. So the better way to program pagination is to say show me items above item n, too item n plus x, where n is a specific post rather than an index. Then you can have dynamic pagination based on the last comment, you saw.

Another way to do this is have your session look at a static snapshot of the dynamic database, until you refresh the page or go back to the top. This is possible with a lot of different databases, kind of like how ZFS can give you snapshots of root at any time.
- I don't know if it is lazy as much as it is a design choice - remember at one point Lemmy actually auto updated (which meant posts were pushed down while you were browsing) and it was an intentional design.
  
  https://github.com/LemmyNet/lemmy/issues/2841#issuecomment-1535469357
  
  It's a valid design choice. But it is to keep the programming simple. One might characterize that kind of choice as lazy. Especially in terms of user interface. But I'm not beating up on Lemmy. I'm just explaining to the original poster the trade-offs that people make.
- “Let’s have each user take an individual snapshot of the database to scroll over until they refresh like in ZFS” ok buddy
  
  Tell me you’ve dabbled in homelab stuff without telling me you’ve never designed a high traffic web backend
  
  Sir, you hardly know me! Disagree fine, but don't assume my pedigree.
  
  FWIW temporal tables, and time travel are real things available now and they are built very similarly to ZFS versioning.
  
  If we are truly trying to make a highly scalable distributed website, we wouldn't be querying a database directly, would be using something distributed. Like foundationDB, or memcached. And we would have to modify our approach somewhat, but these are still solvable problems. The architecture and the requirements are tightly coupled. But we can't make assumptions and rule out solutions at the whiteboard stage.
  
  Why do you have to be so condescending from the get-go? Just explaining why it wouldn't work would have been fine.
I think when a new post is posted and it hits the front page it bumps all the other posts back by that many, which will make them get bumped from the end of one page into the beginning of the next
Next page loads about 3 extra posts for me it seems.
Because new content got posted while you were browsing trough the page. If you refresh the page you're on it shows different entries on the top and the bottom ones are pushed to 2nd page.
- when you start seeing the same posts again and again the deeper you go, that's your cue to start back on page 1 again.
You have your answer from every commenter here but this is why it’s best to browse with an app that marks as read and hides stuff as you scroll.
New posts added since your last refresh push some of current page posts to the next one
The easiest solution might be to just look at what is returned and see if there are any duplicates with what you already have, and just filter those out. It’s not like you’re going to notice if the returned list is shorter if it loads more before you even get to the bottom.

If you get less than 1 screen of posts, ask for more.

You've viewed 19 comments.