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How does Lemmy/Mastodon/Fediverse store videos and images?
(programming.dev)
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this post was submitted on 09 Jul 2023
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Asklemmy
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Edit: I am partially wrong. (See below)
They're stored on their host Instance. Only text is copied across instances.
That is not true. As long as a user on your instance is subscribed to a community, the media content of posts [Edit: only posts linking to outside sources, e.g imgur] of that community is stored locally on your instance as well.
This, of course, only applies to media which is uploaded to Lemmy, links to media hosted externally are not downloaded.
See this issue for more context.
Edit: I want to clarify that I was partially wrong - Lemmy only locally caches content which is hosted on outside sites. It does (should?) not cache content that was directly uploaded to a Lemmy instance and just embeds the source media.
I think this could be a ticking DOS time bomb.
Someone manages to spam upload massive files to the largest Lemmy instances could wipe out a ton of smaller ones.
Not to mention scalability wise this seems like a nightmare… eventually the largest Lemmy instances will have petabytes of media data with 100s of gbs coming in per day, giving other instances no chance to sync with them.
I think the system architecture needs a significant review. This won’t scale.
I agree. It's also a tremendous waste of resources. I'm all for redundancy (like CDNs), but this seems incredibly poorly thought out. If Lemmy (as a whole) every scales to the size of other social media, the space requirements will start to become unreasonable.
Why wouldn't something like symlinks be implemented? Not saying specifically use symlinks, but there has to be a similar, better way.
The obvious way would be to just not cache content locally and always link to the source instance. While this would concentrate the strain immensely, it would also greatly decrease the storage space used by all other instances.
There might also be other viable alternatives such as using a CDN and having it selectively cache content which is requested often etc.
~~As of now, Lemmy does not support either, though. ~~
Edit: I want to clarify that I was partially wrong - Lemmy only locally caches content which is hosted on outside sites. It does (should?) not cache content that was directly uploaded to a Lemmy instance and just embeds the source media.
Agree. If I'm not mistaken, you can only disable the caching of sensitive (NSFW) content on your instance by disabling NSFW in general. This doesn't go for SFW content though.
It shouldn't be very hard to do this for all content though, if I find the time I might look into implementing this.
I feel like the developers should spend some time adding features to reduce malicious activity. They could provide settings to the admins to limit the number of things one user can do in a day, like number of images, total size of images, number of communities created, etc. Sure, someone could create multiple accounts, but it would still make it harder to attack Lemmy.
I mentioned something akin to this possibility a couple days ago, but was told this likely wasn’t the case. I’ll have to see if I can dig up the argument for that.
This actually brings up another question for me! Say your account is on an instance that doesn't allow something, like nudity. If you subscribe to a community on another instance that DOES allow it, you're saying that everything you see there does end up (redundantly) hosted by your home instance. Has the Lemmy moderation/admin community in general decided on whether or not that's breaking the home instance's rules?
Right now you can only disable caching of nsfw content by disabling NSFW for the instance, but of course this has nothing to do with "soft" rules that are only written out in text.
Imo the best solution would be to allow admins to have more granular control over caching, e.g. disabling caching for specific instances / communities or whitelisting. And we need an option to disable caching altogether.
What??? Why? I'll have to shut my instance down if that's true.
I updated my comment as I was partially wrong about what gets cached.
That sounds good for reliability since an instance can still lookup posts even if another fails.
For videos and images, do they store them as blobs in the database or do they use something more catered to files like object storage or maybe a regular filesystem with metadata on a database?
They use pict-rs which looks like it was file system, but is now object storage
That's an awesome name. The Rust community never fails to deliver lol